Method and apparatus for transmitting and receiving signals in optical wireless communication system

ABSTRACT

A method and apparatus for transmitting and receiving signals in a wireless communication system, according to an embodiment of the present invention, may comprise a feature of applying a phase pattern to a wavefront of an optical signal and a feature of transmitting the optical signal. The phase pattern may be determined on the basis of an optical phase shift characteristic of a phase mask, and the phase mask may be determined on the basis of a quantization order and a phase order.

TECHNICAL FIELD

The present disclosure relates to a method and apparatus fortransmitting and receiving signals in an optical wireless communicationsystem. More particularly, the present disclosure relates to a method ofencrypting a wavefront of an optical signal.

BACKGROUND ART

Optical wireless communication systems may be largely divided intovisible light communication (VLC) systems and free-space optical (FSO)communication systems according to the frequency and purpose of photons.

VLC plays the role of lighting and communication at the same time.Information is transmitted by visible light, which may depend on theintensity of the light or the blinking of the light. To this end,visible light devices such as a light emitting diode (LED) is commonlyused.

Free space optical (FSO) communication mainly plays the role ofcommunication and is usually used in a free space environment or anenvironment where signal straightness is guaranteed. The FSOcommunication also covers ultraviolet (UV) and infrared (IR) light aswell as visible light. Unlike VLC, FSO communication is not involved inlighting, so there are no restrictions on lighting. In general, not onlyLEDs but also devices based on the straightness of light such as lightamplification by stimulated emission of radiation (LASER) are used.

On the other hand, conventional optical communication has a disadvantagein that it is difficult to guarantee decoding performance of a receiverdue to the influence from an external interference light source. Inparticular, interference from strong sunlight may significantly reducethe receiver decoding performance. Therefore, there is a need for amethod for transmitting and receiving optical wireless communicationsignals robust to external interference.

In addition, physical layer security in a wireless communication systemcan be effectively used to physically neutralize an eavesdroppingattempt between the transmitter and the receiver. Accordingly, there isa need for a method for transmitting and receiving optical wirelesscommunication capable of providing physical layer security.

DISCLOSURE Technical Problem

An object of the present disclosure is to provide a receiving userequipment (UE) including a demodulator composed of at least one phaseshifter and an optical-to-electrical (O-to-E) converter composed of atleast one photodiode, and a method for efficiently receiving a signal bythe receiving UE.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The present disclosure provides a method and apparatus for transmittingand receiving signals in a wireless communication system.

In an aspect of the present disclosure, there is provided a method oftransmitting and receiving a signal by a first communication apparatusin a wireless communication system. The method may include: applying aphase pattern to a wavefront of an optical signal; and transmitting theoptical signal to a second communication device. The phase pattern maybe determined based on optical phase shift characteristics of a phasemask, and the phase mask may be determined based on a quantization orderand a phase order.

In another aspect of the present disclosure, there is provided a firstcommunication apparatus configured to transmit and receive a signal in awireless communication system. The first communication apparatus mayinclude: at least one transceiver; at least one processor; and at leastone memory operably connected to the at least one processor andconfigured to store instructions that, when executed, cause the at leastone processor to perform operations. The operations may include:applying a phase pattern to a wavefront of an optical signal; andtransmitting the optical signal to a second communication device. Thephase pattern may be determined based on optical phase shiftcharacteristics of a phase mask, and the phase mask may be determinedbased on a quantization order and a phase order.

In another aspect of the present disclosure, there is provided a methodof transmitting and receiving a signal by a second communication devicein a wireless communication system. The method may include: receiving anoptical signal where a phase pattern is applied to a wavefront thereof;and decoding the optical signal. The phase pattern may be determinedbased on optical phase shift characteristics of a phase mask, and thephase mask may be determined based on a quantization order and a phaseorder.

In another aspect of the present disclosure, there is provided a secondcommunication device configured to transmit and receive a signal in awireless communication system. The second communication device mayinclude: at least one transceiver; at least one processor; and at leastone memory operably connected to the at least one processor andconfigured to store instructions that, when executed, cause the at leastone processor to perform operations. The operations may include:receiving an optical signal where a phase pattern is applied to awavefront thereof; and decoding the optical signal. The phase patternmay be determined based on optical phase shift characteristics of aphase mask, and the phase mask may be determined based on a quantizationorder and a phase order.

In another aspect of the present disclosure, there is provided anapparatus for a first communication device. The apparatus may include:at least one processor; and at least one computer memory operablyconnected to the at least one processor and configured to, whenexecuted, cause the at least one processor to perform operations. Theoperations may include: applying a phase pattern to a wavefront of anoptical signal; and transmitting the optical signal to a secondcommunication device. The phase pattern may be determined based onoptical phase shift characteristics of a phase mask, and the phase maskmay be determined based on a quantization order and a phase order.

In a further aspect of the present disclosure, there is provided acomputer-readable storage medium including at least one computer programthat, when executed, causes at least one processor to performoperations. The operations may include: applying a phase pattern to awavefront of an optical signal; and transmitting the optical signal to asecond communication device. The phase pattern may be determined basedon optical phase shift characteristics of a phase mask, and the phasemask may be determined based on a quantization order and a phase order.

In the methods and apparatuses, the quantization order and the phaseorder may be (i) selected by the first communication device or (ii)selected by the second communication device and received by the firstcommunication device.

In the methods and apparatuses, the phase mask may be determined basedon (i) an identifier (ID) of the first communication device or (ii) anID of the second communication device.

In the methods and apparatuses, the phase mask may be used wheninterference to the optical signal is greater than or equal to athreshold. The interference may be (i) measured by the firstcommunication device or (ii) measured by the second communication deviceand received from the second communication device.

In the methods and apparatuses, information on whether the phase mask isused may be (i) transmitted according to a communication method otherthan optical wireless communication or (ii) broadcast through theoptical wireless communication.

In the methods and apparatuses, each of the communication devices mayinclude an autonomous driving vehicle configured to communicate at leastwith a terminal, a network, and another autonomous driving vehicle otherthan the communication device.

It will be understood by those skilled in the art that theabove-described aspects of the present disclosure are merely part ofvarious embodiments of the present disclosure, and various modificationsand alternatives could be developed from the following technicalfeatures of the present disclosure.

Advantageous Effects

As is apparent from the above description, a method for transmitting andreceiving a signal in an optical wireless communication system accordingto the embodiments of the present disclosure can perform physical layerencryption through wavefront encryption. In addition, receptioninterference can be minimized through the wavefront encryption.

The above-described aspects of the present disclosure are merely some ofthe preferred embodiments of the present disclosure, and variousembodiments reflecting the technical features of the present disclosuremay be derived and understood by those skilled in the art based on thefollowing detailed description of the disclosure.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure, illustrate embodiments of thedisclosure and together with the description serve to explain theprinciple of the disclosure.

FIG. 1 is a diagram illustrating an exemplary system for implementingthe present disclosure.

FIG. 2 is a diagram illustrating an exemplary subframe structure inwhich a data channel and a control channel are multiplexed in timedivision multiplexing (TDM).

FIG. 3 is a diagram illustrating the OFDM modulation structure at thetransmitting side of the conventional RF communication system.

FIGS. 4 to 5 are diagrams illustrating the structure of a multi-carriermodulation transmitter of a visible light communication system.

FIGS. 6 to 8 are diagrams illustrating examples of an optical wirelesscommunication system.

FIGS. 9 to 13 are diagram illustrating an optical filter applicable toan optical wireless communication system and a method for acquiring adesired beam using the optical filter.

FIGS. 14 to 16 are diagrams illustrating examples of beam dispersionbased on characteristics of optical resources used by the opticalwireless system.

FIGS. 17 and 18 are diagrams illustrating differences in beam radius andphase characteristics according to an OAM mode of an OAM beam in theoptical wireless communication system.

FIG. 19 is a diagram illustrating a structure of a transceiver of aphysical layer security system based on a wavefront encryption scheme.

FIGS. 20 to 22 are diagrams illustrating a change in phasecharacteristics of an optical beam at a transmitter.

FIGS. 23 to 25 are diagrams illustrating a change in phasecharacteristics of an optical beam at a receiver.

FIG. 26 is a diagram illustrating a structure of a transceiver of aninterference mitigation system based on a wavefront encryption scheme.

FIG. 27 is a diagram illustrating a change in phase characteristics ofan optical beam at a receiver.

FIG. 28 is a diagram illustrating irradiance characteristics of a beamfocused through an optical focusing filter based on phasecharacteristics.

FIG. 29 is a diagram illustrating the change in phase characteristics ofan optical beam at a receiver.

FIGS. 30 and 31 are diagrams illustrating phases of signals affected byambient interference.

FIGS. 32 and 33 are diagrams illustrating a change in phasecharacteristics at a receiver affected by interference from the sun.

FIG. 34 is a diagram illustrating a structure of a transceiver of aninterference mitigation system based on wavefront encryption for use ina system including an orbital angular momentum (OAM) transceiver device.

FIG. 35 is a diagram illustrating a change in phase characteristics ofan OAM-based optical beam at a transmitter.

FIG. 36 is a diagram illustrating a change in phase characteristics ofan OAM-based optical beam at a receiver.

FIG. 37 is a diagram illustrating irradiance characteristics of a beamfocused through an optical focusing filter based on phasecharacteristics.

FIGS. 38 and 39 are diagrams illustrating phases of signals affected byambient interference.

FIGS. 40 to 42 are diagrams illustrating a phase mask informationappointment under control of the transmitter.

FIGS. 43 to 47 are diagrams illustrating a phase mask informationappointment based on measurement and feedback of the receiver.

FIGS. 48 and 49 are diagrams for explaining a quantization order.

FIGS. 50 and 51 are diagrams for explaining a phase order.

FIGS. 52 to 54 are diagrams for explaining phase mask generation.

FIGS. 55 to 57 are diagrams for explaining rules for indicating aquantization order and a phase order.

FIGS. 58 to 63 are diagrams for explaining interference dispersionperformance depending on quantization orders.

FIG. 64 is a diagram for explaining phase mask selection based oninterference recognition.

FIG. 65 illustrates a flowchart according to an embodiment of thepresent disclosure.

BEST MODE

Reference will now be made in detail to the preferred embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. In the following detailed description of thedisclosure includes details to help the full understanding of thepresent disclosure. Yet, it is apparent to those skilled in the art thatthe present disclosure can be implemented without these details. Forinstance, although the following descriptions are made in detail on theassumption that a mobile communication system includes the 3GPP LTE andLTE-A and 5G systems, the following descriptions are applicable to otherrandom mobile communication systems by excluding unique features of the3GPP LTE and LTE-A systems.

Occasionally, to prevent the present disclosure from getting vaguer,structures and/or devices known to the public are skipped or can berepresented as block diagrams centering on the core functions of thestructures and/or devices. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Besides, in the following description, assume that a terminal is acommon name of such a mobile or fixed user stage device as a userequipment (UE), a mobile station (MS), an advanced mobile station (AMS)and the like. In addition, assume that a base station (BS) is a commonname of such a random node of a network stage communicating with aterminal as a Node B (NB), an eNode B (eNB), an access point (AP) andthe like.

In a mobile communication system, a UE can receive information from a BSin downlink and transmit information in uplink. The UE can transmit orreceive various data and control information and use various physicalchannels depending types and uses of its transmitted or receivedinformation.

The following technology may be used in various wireless access systemssuch as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier frequencydivision multiple access (SC-FDMA), and so on. CDMA may be implementedas a radio technology such as universal terrestrial radio access (UTRA)or CDMA2000. TDMA may be implemented as a radio technology such asglobal system for mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA maybe implemented as a radio technology such as institute of electrical andelectronics engineers (IEEE) 802.11 (wireless fidelity (Wi-Fi)), IEEE802.16 (worldwide interoperability for microwave access (WiMAX)), IEEE802.20, evolved UTRA (E-UTRA), and so on. UTRA is a part of universalmobile telecommunications system (UMTS). 3rd generation partnershipproject (3GPP) long term evolution (LTE) is a part of evolved UMTS(E-UMTS) using E-UTRA, and LTE-advanced (LTE-A) is an evolution of 3GPPLTE.

Moreover, in the following description, specific terminologies areprovided to help the understanding of the present disclosure. And, theuse of the specific terminology can be modified into another form withinthe scope of the technical idea of the present disclosure.

FIG. 1 is a diagram illustrating a system for implementing the presentdisclosure.

Referring to FIG. 1 , a wireless communication system includes a BS 10and one or more UEs 20. On downlink (DL), a transmitter may be a part ofthe BS 10 and a receiver may be a part of the UE 20. On uplink (UL), theBS 10 may include a processor 11, a memory 12, and a radio frequency(RF) unit 13 (transmitter and receiver). The processor 11 may beconfigured to implement the proposed procedures and/or methods disclosedin the present application. The memory 12 is coupled to the processor 11to store a variety of information for operating the processor 11. The RFunit 13 is coupled to the processor 11 to transmit and/or receive radiosignals. The UE 20 may include a processor 21, a memory 22, and an RFunit 23 (transmitter and receiver). The processor 21 may be configuredto implement the proposed procedures and/or methods disclosed in thepresent application. The memory 22 is coupled to the processor 21 tostore a variety of information for operating the processor 21. The RFunit 23 is coupled to the processor 21 to transmit and/or receive radiosignals. The BS 10 and/or the UE 20 may include a single antenna andmultiple antennas. If at least one of the BS 10 or the UE 20 includesmultiple antennas, the wireless communication system may be called amultiple input multiple output (MIMO) system.

In the present specification, although the processor 21 of the UE andthe processor 11 of the BS perform an operation of processing signalsand data, except for a function of receiving or transmitting signals anda function of storing signals, the processors 11 and 21 will not beespecially mentioned for convenience of description. Even though theprocessors 11 and 21 are not particularly mentioned, it may be said thatthe processors 11 and 21 perform operations of processing data exceptfor a function of receiving or transmitting signals.

The present disclosure proposes various new frame structure for a 5thgeneration (5G) communication system. In the next generation 5G system,communication scenarios are classified into Enhanced Mobile Broadband(eMBB), Ultra-reliability and low-latency communication (URLLC), MassiveMachine-Type Communications (mMTC), etc. Here, eMBB is the nextgeneration mobile communication scenario having such properties as HighSpectrum Efficiency, High User Experienced Data Rate, High Peak DataRate and the like, URLLC is the next generation mobile communicationscenario having such properties as Ultra Reliable, Ultra Low Latency,Ultra High Availability and the like (e.g., V2X, Emergency Service,Remote Control), and mMTC is the next generation mobile communicationscenario having such properties as Low Cost, Low Energy, Short Packet,Massive Connectivity and the like (e.g., IoT).

FIG. 2 is a diagram illustrating an exemplary subframe structure inwhich a data channel and a control channel are multiplexed in timedivision multiplexing (TDM). In 5G NR, a frame structure in which acontrol channel and a data channel are multiplexed according to TDM likeFIG. 2 may be considered in order to minimize latency.

In FIG. 2 , the hatched area represents a transmission region of a DLcontrol channel carrying DCI (e.g., PDCCH), and the last symbolrepresents a transmission region of a UL control channel carrying UCI(e.g., PUCCH). Here, the DCI is control information transmitted from agNB to a UE and may include information on a cell configuration the UEshould know, DL-specific information such as DL scheduling, UL-specificinformation such as a UL grant, etc. The UCI is control informationtransmitted from the UE to the gNB and may include a HARQ ACK/NACKreport on DL data, a CSI report on a DL channel state, a schedulingrequest (SR), etc.

In FIG. 2 , blank areas are available for flexible configuration of DLor UL periods to achieve DL/UL flexibility. For example, a blank areamay be used as a data channel for DL data transmission (e.g., a physicaldownlink shared channel (PDSCH)) or a data channel for UL datatransmission (e.g., a physical uplink shared channel (PUSCH)). Thisstructure is characterized in that since a DL transmission and a ULtransmission may be performed sequentially in one subframe, an eNB maytransmit DL data in the subframe to a UE and receive an HARQ ACK/NACKsignal for the DL data in the subframe from the UE. That is, the timerequired to retransmit data when a data transmission error occurs may bereduced, thereby minimizing the latency of final data transmission.

In the self-contained subframe structure, a time gap is necessary inorder that the gNB and UE switch to a reception mode from a transmissionmode, and vice versa. For the switching between the transmission modeand the reception mode, some OFDM symbols at the time of DL-to-ULswitching may be configured as a guard period (GP) in the self-containedsubframe structure.

In the case of an optical wireless communication system, there aregenerally single carrier modulation (SCM) methods based on-off keying(OOK) that represents signals based on flickering of visible light. InOOK modulation, digital signals 1 and 0 can be expressed according to ONand OFF states of the light source. OOK modulation can be modified by amodulation scheme such as pulse position modulation (PPM) whichmodulates an input signal into a clock-based pulse position.

Regarding the visible light communication system, research onmulti-carrier modulation (MCM) schemes have been conducted. Compared tothe single carrier modulation scheme, the MCM scheme is robust tomultipath, and enables operation of a single tap equalizer. It is alsorobust to DC wandering and flickering interference. The MCM-basedwaveform for VLC must satisfy the conditions that i) it has only onedimension (real-value) signal and ii) it has unipolar characteristics.

FIG. 3 is a diagram illustrating the OFDM modulation structure at thetransmitting side of the RF communication system. Referring to FIG. 3 ,an analog signal obtained through OFDM modulation is amplified throughan RF power amplifier (PA). In this case, the maximum amplifiedmagnitude of the signal may be limited by the performance limit of thePA.

On the other hand, the structure of a multi-carrier modulationtransmitter of the visible light communication system as shown in FIGS.4 to 5 . More specifically, FIG. 4 shows the structure of a DCO-OFDMmodulation transmitter of the VLC communication system, and FIG. 5 showsthe structure of an ACO-OFDM modulation transmitter of the VLCcommunication system. In FIGS. 4 and 5 , when an electrical-to-optical(E-to-O) device designed to use a band (e.g., an infrared band) otherthan visible light such as laser light emitted from LEDs is used in theedge device, the above-described situation may correspond to the rangeof free space optical communication.

FIG. 6 is a diagram illustrating a basic structure of an opticalwireless communication system. In the basic structure of FIG. 6 , thetransmitter may transmit radio light, and the receiver may decode theradio light.

Referring to FIG. 6 , the transmitter converts data to be transmitted(e.g., electrical signal) into a photon (optical) source by anelectrical-to-optical (E-to-O) device and transmits the photon source tothe receiver in a wireless environment. The photon source may bereferred to as radio light.

Here, the radio light may be interpreted as a wave corresponding to aset of photons and classified into a plane wave and a spherical waveaccording to the shape of a wavefront. The plane wave refers to a wavewith a straight or planar wavefront. For example, the plane wave may beartificially generated by resonance as in a laser beam. The sphericalwave refers to a wave in which the wavefront forms a concentricspherical surface around a wave source when the wave source is a pointin space. When the spherical wave propagates away, wavefronts are almostparallel to each other, so that the spherical wave may be regarded asthe plane wave from the viewpoint of the receiver.

When the receiver receives a desired optical signal including data in awireless environment, the receiver may receive i) interference fromother sources and ii) solar interference from the sun along with thedesired optical signal. The receiver may decode the desired opticalsignal into the data based on i) an optical filter for determining theradio light used for the desired optical signal, ii) an O-to-E devicethat converts the receiver radio light into an electrical signal, andiii) direct detection for analyzing the signal.

On the other hand, according to an example or implementation of thepresent disclosure shown in FIG. 7 , the transmitter may transmit to thereceiver in a wireless environment by i) converting data to betransmitted (e.g., electrical signal) into a photon source with anE-to-O device and ii) generating an optical beam with an optical beamgenerator.

In optics, radio light may be represented as a beam. In an example orimplementation of the present disclosure, a case in which an opticalbeam is configured based on a transverse electromagnetic field/wave(TEM) mode corresponding to a resonant mode among transverse modes ofelectromagnetic radiation will be described.

The TEM mode may be divided into TEM1m by indices 1 and m according tobeam formation. In general, the basic form of the TEM mode is a Gaussianbeam, which is represented by TEM00. TEM00 refers to an optical beam inwhich a wave amplitude distribution on a cross-section perpendicular toan optical axis is expressed by a Gaussian function.

When the receiver receives a desired optical beam including data in awireless environment, the receiver may receive i) interference fromother sources and ii) solar interference from the sun along with thedesired optical signal. The receiver may decode the desired optical beaminto the data based on i) an optical filter for determining the radiolight used for the desired optical beam, ii) an O-to-E device thatconverts the receiver radio light into an electrical signal, and iii)direct detection for interpreting the signal.

Next, initial access based on legacy links and initial access based onbroadcast messages will be described.

1.1. Initial Access Based on Legacy Link

A transmitting UE and receiving UE may share initial information foroptical wireless communication through legacy links (e.g., LTE, LTE-A,NR, WiFi, Bluetooth, etc.). The initial information for optical wirelesscommunication may include the following.

i) Band for transmission and reception: This may mean a frequency bandor light wavelength range for transmission and reception of data andcontrol information.

ii) Polarization for transmission and reception: This may mean apolarization direction for transmission and reception of data andcontrol information. For example, it may be agreed between thetransmitting UE and receiving UE that data and control information isexchanged based on only vertical polarization for interference control.

iii) OAM mode for transmission and reception: This may mean an OAM modeindex for transmission and reception of data and control information.

iv) Baseband modulation for transmission and reception: This may mean abaseband modulation method for transmission and reception of data andcontrol information. For example, for data modulation and demodulation,i) an on/off keying (OOK) method may be used for single carriermodulation, or ii) an orthogonal frequency-division multiplexing (OFDM)method may be used as for multi-carrier modulation, which may be agreedbetween the transmitting UE and receiving UE.

1.2. Initial Access Based on Broadcast Message

A transmitting UE and receiving UE may share initial information basedon broadcast messages. For example, the transmitting UE and receiving UEmay broadcast a predetermined broadcast message on an optical or radioresource as in broadcast over a physical broadcast channel (PBCH) orcommon control channel of LTE/LTE-A in order to share the initialinformation for optical wireless communication. The initial informationfor optical wireless communication may be as follows.

i) Band for transmission and reception: This may mean a frequency bandor light wavelength range for transmission and reception of data andcontrol information.

ii) Polarization for transmission and reception: This may mean apolarization direction for transmission and reception of data andcontrol information. For example, it may be agreed between thetransmitting UE and receiving UE that data and control information isexchanged based on only vertical polarization for interference control.

iii) OAM mode for transmission and reception: This may mean an OAM modeindex for transmission and reception of data and control information.

iv) Baseband modulation for transmission and reception: This may mean abaseband modulation method for transmission and reception of data andcontrol information. For example, for data modulation and demodulation,i) an OOK method may be used for single carrier modulation, or ii) anOFDM method may be used as for multi-carrier modulation, which may beagreed between the transmitting UE and receiving UE.

2.1. Next, “Optical Wireless Broadband Communication Transmitter andReceiver Based on Photon OAM” Will be Described in Detail.

In an example or implementation of the present disclosure shown in FIG.8 , proposed is a system including: i) a transmitting UE transmitting asignal based on a photon OAM beam generator; and ii) a receiving UEusing an optical filter for distinguishing a desired OAM beam fromoptical interference. According to the proposed system, it is possibleto minimize interference from sunlight or other sources having the sameband and same polarization as those of a desired optical beam.

If radio light is interpreted as an electromagnetic wave, the TEM modemay be classified depending on to the shape of a beam. The basic form ofthe TEM mode is generally a Gaussian beam, which is represented byTEM00. Hermite-Gaussian (HG) modes with rectangular transverse modepatterns are represented by TEMmn. LG modes with cylindrical transversemode patterns are represented by TEMp1. In an example or implementationof the present disclosure, the LG modes (TEMp1) may be represented byphoton OAM.

2.2. Transmitting UE

A transmitting UE may convert an electric source including data to betransmitted into an optical source with an E-to-O device. The convertedoptical source may be converted into a photon OAM beam by a photon OAMbeam generator as follows.

i) The transmitting UE may convert the optical source into a Gaussianbeam (TEM00) by passing the optical source through a resonator and thenconvert the Gaussian beam into the photon OAM beam (TEMp1) with a spiralphase plate.

ii) The transmitting UE may convert the optical source to a Gaussianbeam (TEM00) by passing the optical source through a resonator, andconvert the Gaussian beam into the photon OAM beam (TEMp1) by reflectingthe Gaussian beam on a phase hologram with a spiral phase pattern.

iii) The transmitting UE may convert the optical source to a Gaussianbeam (TEM00) by passing the optical source through a resonator andconvert the Gaussian beam into the photon OAM beam (TEMp1) by reflectingthe Gaussian beam on a phase hologram with a fork diffraction pattern.

iv) The transmitting UE may convert the optical source to aHermite-Gaussian beam (TEMmn) by passing the optical source through aresonator and convert the Hermite-Gaussian beam into the photon OAM beam(TEMp1) by passing the Hermite-Gaussian beam through a cylindrical lensHG-LG mode converter (e.g., pi/2 mode converter).

In addition to methods i) to iv) described above, various methodscapable of generating a photon OAM beam may be applied to examples orimplementations of the present disclosure.

2.3. Receiving UE

2.3.1. Optical Filter

An optical filter provided in a receiving UE may include a generaloptical filter or a polarizing filter. The general optical filter is anoptical element for receiving a band corresponding to a desired opticalbeam. The optical filter may include a filter that transmits with aconstant transmittance regardless of wavelengths, a correction filterthat controls light intensity in a specific wavelength range, and alight contrast filter. The optical filter may be classified into aninfrared range filter, a visible range filter, an ultraviolet rangefilter, a vacuum ultraviolet range filter, and so on depending onfrequency ranges. Filters in each range may have different materials andstructures.

Alternatively, the optical filter may be a polarized light filter(polarization filter). The polarization filter is a filter based onpolarization, i.e., a filter for passing only light vibrating in aspecific direction in order to receive polarized light corresponding toa desired optical beam. In general, polarization mainly occurs whenobliquely projection light is reflected from a uniform surface.Therefore, if the polarization filter is used to block light reflectedfrom the surface of a glass window or object, a clear and sharp imagemay be obtained. For example, a camera has a polarization filter capableof adjusting and rotating a polarization direction. If an autofocuscamera uses the polarization filter, the autofocus camera may notrecognize light and thus lose a focus because only wavelengths vibratingin one direction remain. A solution to this phenomenon is a circularpolarization filter.

2.3.2. Lens

A lens is a device for focusing a received optical source to a focalpoint based on the effect of refraction.

2.3.2.1. Focal Point Control Based on Wavelength

Referring to FIG. 9 , an optical source passing through a convex lens ora Fresnel lens has different focal points depending on wavelengths.Based on this characteristic, the receiving UE may control the intensityconcentration of the optical source received on a photodiode array. Thephotodiode array according to an example or implementation of thepresent disclosure refers to an array in which a plurality of lightreceiving elements performing O-to-E conversion are distributed in aspecific area.

For example, when the focal point of green light is denoted by fgreen inFIG. 9 , the focal points of blue light and red light are fblue andfred, respectively. It may be seen that the blue light, green light, andred light have different focal points. Based on this characteristic, thereceiving UE may control the intensity of green light to be concentratedat the center of the photodiode array, the intensity of red light tospread over a larger area, and the intensity of blue light to spreadover a further larger area.

Based on the above control, the receiving UE may receive a green lightsignal at the focal point of the green light more efficiently. Thereceiving UE may control focal points depending on wavelengths by i)controlling the thickness of the convex lens or Fresnel lens or ii)controlling the distance between the convex lens and the photodiodearray.

2.3.2.2. Focal Point Control Based on OAM Mode

Referring to FIG. 10 , an OAM optical source passing through a lens withan arbitrary refraction angle (e.g., Fresnel lens) has different focalpoints depending on mode indexes. Based on this characteristic, thereceiving UE may control the intensity concentration of OAM modesreceived on the photodiode array.

For example, it may be seen from FIG. 10 that OAM mode +1, OAM mode 0,and OAM mode −1 have different focal points. In OAM mode 0, thereceiving UE may control the intensity to be concentrated at the centerof the photodiode array. In OAM mode −1, the receiving UE may controlthe intensity to spread over a larger area. In OAM mode +1, thereceiving UE may control the intensity to spread over a further largerarea.

When the focal point of OAM mode 0 is f₀, the focal point of mode indexm, f_(m) may be approximated as follows: f_(m)=f₀ (1+C·m), whereconstant C is an OAM dispersion coefficient.

The receiving UE may control the focal points of OAM modes by i)controlling the thickness of the lens or Fresnel lens or ii) controllingthe distance between an arbitrary lens and the photodiode array.

2.3.3. Fresnel Zone Plate

A Fresnel zone plate is a device for focusing a received optical sourceto a focal point based on the effect of diffraction. Specifically, thezone plate or Fresnel zone plate is a device for focusing materials withlight or wave characteristics. Unlike lenses or curved mirrors, the zoneplate may use diffraction instead of reflection and refraction. The zoneplate consists of a set of radially symmetric rings that alternatebetween opaque and transparent areas, which is known as a Fresnel zone.Light hitting the zone plate is diffracted around an opaque area. Theareas may be spaced apart so that diffracted light structurallyinterferes at a desired focal point to produce an image.

It may be seen from FIG. 11 that an optical source passing through theFresnel zone plate have different wave characteristics or have differentintensity distributions in a focal plane depending on OAM mode indexes.Based on these characteristics, the receiving UE may control theintensity distribution of the optical source received on the photodiode.

Referring to FIG. 11 , when the optical source passing through theFresnel zone plate is i) natural light such as sunlight or ii) planewave light such as linearly polarized light or circularly polarizedlight, the intensity thereof may be concentrated at the center of thefocal plane of the Fresnel zone plate.

When the optical source passing through the Fresnel zone plate is aplane wave light beam and a Gaussian beam, the intensity of the opticalsource may be distributed with a Gaussian distribution with respect tothe center of the photodiode, which is located at the focal plane of theFresnel zone plate.

When the optical source passing through the Fresnel zone plate is an LGbeam corresponding to helical wave light, the intensity may bedistributed in the form of a ring with respect to the center of thephotodiode located at the focal plane of the Fresnel zone plate whilemaintaining the characteristics of an OAM state.

For example, in FIG. 11 , OAM mode 0, OAM mode +3, and OAM mode +5 havedifferent intensity distributions. In OAM mode 0, the receiving UE maycontrol the intensity to be concentrated at the center of the photodiodewith the Gaussian distribution. In OAM mode +3, the receiving UE maycontrol the intensity to spread over a larger area in the form of aring, In OAM mode +5, the receiving UE may control the intensity tospread over a further larger area in the form of a ring. In this case,for general plane wave light such as i) natural light such as sunlightand ii) linearly polarized or circularly polarized light, the intensitythereof may be concentrated in a very small area at the center of thephotodiode. This area is smaller than the area in OAM mode 0 where theintensity is distributed at the center of the photodiode with theGaussian distribution.

The receiving UE may control the intensity distribution of the opticalsource received on the photodiode by i) controlling a pattern accordingto the ring configuration of the Fresnel zone plate or ii) controllingthe distance between the Fresnel zone plate and the photodiode.

2.3.4. Photon Sieve

A photon sieve is a device for focusing a received optical source to afocal point based on diffraction and interference effects. The photonsieve may include a flat sheet filled with pinholes arranged in apattern similar to the ring of the Fresnel zone plate described above.The photon sieve may provide a much sharper focal point than the zoneplate. The photon sieve is manufactured to include pinholes with varioussizes and patterns and the characteristics of the focal point operationmay vary depending on applications, so that the photon sieve may be usedin various ways.

The receiving UE may control the intensity distribution of the opticalsource received on the photodiode based on i) wave characteristics ofthe optical source passing through the photon sieve or ii) thecharacteristic that the intensity distribution at the focal plane variesaccording to the OAM mode index.

When the optical source passing through the photon sieve is i) naturallight such as sunlight or ii) plane wave light such as linearly orcircularly polarized light, the intensity of the optical source may beconcentrated at the center of the photodiode array located at the focalplane of the photon sieve.

When the optical source passing through the photon sieve is a plane wavelight beam and a Gaussian beam, the intensity of the optical source isdistributed with a Gaussian distribution with respect to the center ofthe photodiode array located at the focal plane of the photon sieve.

When the optical source passing through the photon sieve is an LG beamcorresponding to helical wave light, the intensity may be distributed inthe form of a ring with respect to the center of the photodiode arraylocated at the focal plane of the photon sieve while maintaining thecharacteristics of an OAM state.

For example, in FIG. 12 , OAM mode 0, OAM mode +3, and OAM mode +5 havedifferent intensity distributions. In OAM mode 0, the receiving UE maycontrol the intensity to be concentrated at the center of the photodiodewith the Gaussian distribution. In OAM mode +3, the receiving UE maycontrol the intensity to spread over a larger area in the form of aring, In OAM mode +5, the receiving UE may control the intensity tospread over a further larger area in the form of a ring. In this case,for general plane wave light such as i) natural light such as sunlight,and ii) linearly polarized or circularly polarized light, the intensitythereof may be concentrated in a very small area at the center of thephotodiode. This area is smaller than the area in OAM mode 0 where theintensity is distributed at the center of the photodiode with theGaussian distribution.

The receiving UE may control the intensity distribution of the opticalsource received on the photodiode array by i) controlling a patternaccording to the pinhole configuration of the photon sieve or ii)controlling the distance between the photon sieve and the photodiodearray.

2.3.5. Phase Mask

A phase mask is a device for controlling a propagation directionaccording to the characteristics of a received optical source based onthe effect of diffraction. The phase mask may include optical elements.

The receiving UE may control the position of the intensity distributionof the optical source received on the photodiode array based on i) thewave characteristics of the optical source passing through the phasemask (or pattern mask) or ii) the characteristic that the propagationdirection of a beam changes depending on the OAM mode index.

For example, it may be seen from FIG. 13 that OAM mode 0, OAM mode +2,OAM mode −2, and OAM mode +3 have different intensity distributionpositions. In this case, since general plane wave light such as i)natural light such as sunlight and ii) linearly or circularly polarizedlight has the same phase characteristics as a plane wave of OAM mode 0,the intensity thereof may be distributed in the third quadrant of areceiving plane in which the intensity distribution of OAM mode 0 islocated. On the other hand, a lens serves to focus the optical sourcepassing through the phase mask on the receiving plane.

The receiving UE may control the position of the intensity distributionof the optical source received on the photodiode array by i) controllingthe phase elements constituting the phase mask or ii) controlling thedistance between the phase mask and the photodiode array, the distancebetween the phase mask and the lens, and/or the distance between thelens and the photodiode array.

According to an example or implementation of the present disclosure, twoor more of the above-described optical filters (e.g., lens, Fresnel zoneplate, photon sieve, and phase mask) may be combined and applied toobtain each characteristic multiply. For example, the receiving UE mayi) receive a specific wavelength with the general optical filter tocontrol its received wavelength, ii) receive desired polarized lightwith the polarization filter, and iii) distinguish plane wave and spiralwave modes based on the characteristics of wave light with the photonsieve.

3.1. Divergence Angle of Gaussian Beam

FIG. 22 is a diagram for explaining the dispersion angle of a Gaussianbeam in a far field. The dispersion angle of the Gaussian beam may bedefined as shown in [Equation 1] below. In Equation 1, k_(o) is a wavevector with a value of 2pi/lambda, and wo is a minimum beam waist, whichmay vary depending on beam formation.

$\begin{matrix}{\frac{\theta_{o}}{2} = {\frac{2}{k_{o}w_{v}} = \frac{\lambda}{\pi w}}} & \left\lbrack {{Equation}1} \right\rbrack\end{matrix}$

It is assumed that M2 is set to 1 (M2=1) when the transmitting UE formsa beam by optimally designing an M2 factor. Referring to FIG. 22 , i)when waist=658 um and wavelength=700 nm, angle=338.6 urad (i.e., 0.0194degrees). In addition, ii) when waist=375 um and wavelength=400 nm,angle=338.6 urad (i.e., 0.0194 degree). In this case, the radius of thebeam is 3.4 mm at a distance of 10 m (distance=10m).

3.2. Divergence Angle of LG Beam

FIGS. 23 and 24 are diagrams for explaining the divergence angle of anLG beam in a far field. The divergence angle of the LG beam is definedbased on [Equation 2] to [Equation 4] below. Specifically, [Equation 2]shows a case where wo is fixed, and [Equation 4] shows a case wherer_(ms)(0) is fixed. Here, k_(o) is a wave vector with a value of2pi/lambda, and w_(o) is a minimum beam waist, which may vary dependingon beam formation. The relationship between ko and wo may be defined asshown in [Equation 5]

$\begin{matrix}{\alpha_{\ell} = {\sqrt{\frac{{❘\ell ❘} + 1}{2}}\frac{2}{k_{0}w_{0}}}} & \left\lbrack {{Equation}2} \right\rbrack\end{matrix}$ $\begin{matrix}{\alpha_{t} = \frac{{❘\ell ❘} + 1}{k_{0}{r_{rms}(0)}}} & \left\lbrack {{Equation}3} \right\rbrack\end{matrix}$ $\begin{matrix}{{r_{rms}(0)} = {\sqrt{\frac{{❘\ell ❘} + 1}{2}}w_{0}}} & \left\lbrack {{Equation}4} \right\rbrack\end{matrix}$

It is assumed that M2 is set to 1 (M2=1) when the transmitting UE formsa beam by optimally designing an M2 factor. Referring to FIG. 23 , theradius of the beam may appear as shown in FIG. 23 at a distance of 10 m(distance=10m) according to Ill. Referring to FIG. 24 , in the case ofan OAM beam, the beam radius may vary depending on OAM order 1. Also,the beam size (e.g., beam radius) at the receiving UE may vary dependingon the distance between the transmitting UE and receiving UE.

On the other hand, phase characteristics of the received wavefront mayvary depending the OAM Order 1. For example, as shown in FIG. 17 , aphase difference for an E-field may occur in accordance with OAM orders(or Modes). In this case, the term “phase” may indicate a change overtime when viewed from the propagation direction of the light source in asituation where the E-field is represented by sine waves. Specifically,when the Y-axis of FIG. 18 indicates the vibration direction of theE-field, vibration of the E-field can be expressed as shown in FIG. 18 .In FIG. 18 , the graph depicting the E-field vibration over time mayindicate the movement direction of light (i.e., the optical axis), andmay represent the phase change over time. The change in phase may bedetermined by a wavelength (2) corresponding to one cycle, and the time(t) is a unit for a time during which the light travels, and the time(t=λ/c) (where c=2.99792458*10⁸ m/s, luminous flux) during which thelight travels by the distance corresponding to one cycle. Therefore, forattributes indicating that phase characteristics of the receivedwavefront vary depending on the OAM Order 1, the receiver must performcoherent combining while performing phase compensation. In addition,reception (Rx) decoding performance can be increased by changing thedesign of the receiver.

All of the above-described data transmission methods may have difficultyin guaranteeing decoding performance of the receiver due to theinfluence from an external interference light source. In particular,interference from strong sunlight may significantly reduce the decodingperformance of the receiver. Therefore, there is a need for a method fortransmitting and receiving optical wireless communication robust toexternal interference.

In addition, physical layer security in a wireless communication systemcan be effectively used to physically neutralize an eavesdroppingattempt by a person who tries to eavesdrop between the transmitter andthe receiver. Accordingly, there is a need for a method for transmittingand receiving optical wireless communication capable of providingphysical layer security.

The present disclosure provides a method for performing wavefrontencryption based on a phase mask in optical wireless communication.

3.1. Physical Layer Security System Based on Wavefront Encryption

In the system according to the present disclosure, according to apredefined agreement between a transmitter and a receiver, thetransmitter may perform wavefront encryption through a phase mask, andthe receiver may perform wavefront decryption through an inverse phasemask of the phase mask applied at the transmitter.

The transceiver structure of the physical layer security system based onwavefront encryption is as shown in FIG. 19 . In FIG. 19 , thetransmitter may convert data for optical wireless communication into anoptical resource, and the converted optical resource (e.g., an opticalbeam) passes through the phase mask so that a phase pattern of the phasemask can be applied to the wavefront. For example, in the transmitter,the phase characteristics of the optical beam can be converted as shownin FIG. 20 .

In FIG. 20 , it is assumed that the gray color denotes “Phase=0”, theblack color denotes “Phase=n”, and the white color denotes “Phase=−π”.Assuming that the phase of a wavefront of an optical beam having passedthrough the electrical-to-optical (E-to-O) device of the transmitter isan in-phase plane wave (e.g., Gaussian beam), the phase of the wavefrontcan be depicted in the (x, y) two-dimensional plane as shown in the leftview of FIG. 20 . When the optical beam passes through a phase mask (seethe middle view of FIG. 20 ) having a specific pattern, a desiredoptical beam may have the shape of an encrypted wavefront as shown inthe right view of FIG. 20 . That is, the wavefront plane is depicted asa wavefront composed of a specific pattern in the in-phase plane waves.For example, it is assumed that, when the z axis is referred to as atime axis (i.e., the traveling direction of the optical beam, or theoptical axis) as shown in FIG. 21 , the optical beam having the shape ofa plane wave has passed through the phase mask by which a phase ischanged based on a delay. Then, as shown in FIG. 21 , the phase of theencrypted wavefront is changed according to delay characteristics of thephase mask so that the wavefront can be formed.

In FIG. 21 , when the phase of a portion of the beam having passedthrough the medium having a specific length corresponding to “Delay=b”is zero ‘0’, the phase of a portion of the beam (e.g., the beamcorresponding to “Delay=a”) having passed through the shorter medium canbe shifted by “−π”, and the phase of a portion of the beam having passedthrough the longer medium (e.g., the beam corresponding to “Delay=c”)can be shifted by “π”. Since the above-described concepts are applied toboth the X-axis and the Y-axis, the optical beam can be encryptedaccording to the phase pattern when viewed from the (x, y)two-dimensional (2D) plane of the wavefront.

Referring to FIG. 22 , a phase mask may be formed through at least onephase shifter (e.g., a phase shifter array), and each portion of asingle phase shifter may also be formed to perform functions ofdifferent phase shifters. In the latter case indicating that therespective portions of the phase shifter are configured to perform thefunctions of different phase shifters, when an optical beam isirradiated to a hologram using the optical element designed to use ahologram pattern, the phase of the reflected optical beam can bedeformed.

On the other hand, the receiver receives the encrypted optical beam andallows the received beam to penetrate the inverse phase mask forcompensating for the phase pattern used for encryption at thetransmitter, thereby converting the encrypted wavefront into theoriginal planar wave. For example, in the receiver, the phasecharacteristics of the optical beam can be converted, as shown in FIG.23 .

In FIG. 23 , it is assumed that the gray color denotes “Phase=0”, theblack color denotes “Phase=n”, and the white color denotes “Phase=−π”.The phase of the encrypted wavefront received in the receiver can bedepicted in the (x, y) two-dimensional plane as shown in the left viewof FIG. 23 . When the encrypted optical beam passes through an inversephase mask (see the middle view of FIG. 23 ) corresponding to a phasemask of a specific pattern used in the transmitter, the encryptedoptical beam may have the shape of a decrypted wavefront as shown in theright view of FIG. 23 . That is, the wavefront plane is depicted as aplane wave having an in-phase in a wavefront composed of a specificpattern. For example, it is assumed that, when the z axis is referred toas a time axis (i.e., the traveling direction of the optical beam, orthe optical axis) as shown in FIG. 24 , the encrypted optical beamhaving the shape of an encrypted wavefront to which the phase of aspecific pattern is applied has passed through the inverse phase mask bywhich the phase is changed based on a delay. Then, as shown in FIG. 21 ,the phase of the decrypted wavefront is changed according to delaycharacteristics of the inverse phase mask so that the wavefront havingthe shape of plane waves can be formed.

In FIG. 24 , when the phase of a portion of the beam having passedthrough the medium having a specific length corresponding to “Delay=b”is zero ‘0’, the phase of a portion of the beam (e.g., the beamcorresponding to “Delay=a”) having passed through the shorter medium canbe shifted by “−π”, and the phase of a portion of the beam having passedthrough the longer medium (e.g., the beam corresponding to “Delay=c”)can be shifted by “π”. As a result, the phase of each point of thedeformed encrypted wavefront is compensated to zero ‘0’ at thetransmitter, so that the phase of the decrypted wavefront can reach thein-phase state and indicates the shape of a plane wave. Since theabove-described concepts are applied to both the X-axis and the Y-axis,the encrypted optical beam can be encrypted according to the inversephase pattern when viewed from the (x, y) two-dimensional (2D) plane ofthe wavefront.

Referring to FIG. 25 , in the above-described concept, the inverse phasemask may form at least one phase mask (i.e., the structure of a phaseshifter array), and a single phase shifter may be formed to perform afunction of another phase shifter that is partially different in shape(i.e., an optical element designed to use a hologram pattern, so that,when the optical beam is irradiated to the hologram, the phase of thereflected optical beam may be deformed).

Through the above-described method, a physical layer security functioncan be performed in the optical wireless communication system. Forexample, when the eavesdropper attempts to perform decryption bystealing or branching a desired optical beam, if the eavesdropper doesnot know information of the phase mask that has been used in thetransmitter, it may be impossible to perform decryption. Accordingly,information about the phase mask promised between the transmitter andthe receiver may allow the function of a physical layer encryption keyto be made available.

3.2. Wavefront Encryption-Based Interference Mitigation System

The system according to the present disclosure may allow the transmitterto perform a wavefront encryption through a phase mask according to apredefined promise between the transmitter and the receiver, may allowthe receiver to perform wavefront decryption through the inverse phasemask of the phase mask applied to the transmitter, and may mitigateinterference by performing optical focusing through the optical filterdesigned to use phase characteristics.

The transceiver structure of the interference mitigation system based onthe wavefront encryption is as shown in FIG. 26 . As described above inSection 1, the transmitter may convert data for optical wirelesscommunication into an optical resource, and the converted opticalresource (e.g., the optical beam) may pass through the phase mask, sothat a phase pattern of the phase mask can be applied to the wavefront.The desired optical beam having passed through the phase mask formed tohave a particular pattern may have the shape of an encrypted wavefront.In addition, as described above in Section 1, the receiver may receivethe encrypted optical beam, the encrypted optical beam may pass throughthe inverse phase mask formed to compensate for the phase pattern usedfor encryption at the transmitter, so that the encrypted wavefront canbe converted into the original plane waves. The original plane waveconverted into the original plane wave may perform optical focusingthrough the optical filter (e.g., Fresnel Zone Plate, Photon Sieve,etc.) designed to use phase characteristics. For example, in thereceiver, the phase characteristics of the optical beam can be convertedas shown in FIG. 27 .

In FIG. 27 , it is assumed that the gray color denotes “Phase=0”, theblack color denotes “Phase=π”, and the white color denotes “Phase=−π”.However, referring to the Fresnel zone plate shown in FIG. 27 , theblack color denotes a physically blocked space (i.e., the opticalresource cannot pass through the blocked space) regardless of the phase,and the white color denotes a physically opened space (i.e., the opticalresource can pass through the opened space) regardless of the phase. Thephase of the encrypted wavefront received in the receiver can bedepicted in the (x, y) two-dimensional plane as shown in the left-firstview of FIG. 27 . When the encrypted optical beam passes through theinverse phase mask (i.e., the left-second view of FIG. 27 )corresponding to the specific-patterned phase mask used at thetransmitter, the encrypted optical beam may have the shape of adecrypted wavefront corresponding to the left-third view of FIG. 27 .That is, the wavefront plane is depicted as a plane wave in which thephase of a wavefront having a specific pattern is at the in-phase. Whenthe decrypted wavefront formed in the plane wave passes through theoptical focusing filter (such as the Fresnel zone plate) based on thephase characteristics, there may appear irradiance characteristics ofthe focused beam incident upon the O-to-E device (e.g., the photodiode)as shown in FIG. 28 .

In FIG. 28 , the left view represents a focused beam represented by the(x, y) two-dimensional plane. In FIG. 28 , the white color denotes thearea of the optical beam having the strongest irradiance, and the blackcolor denotes the area of the optical beam having the weakestirradiance. When the intensity of irradiance is represented by theZ-axis, the intensity of irradiance can be expressed as athree-dimensional (3D) irradiance as shown in the middle view of FIG. 28. An example of measuring the intensity of irradiance is shown in theright view of FIG. 28 . That is, if the plane wave-shaped decryptedwavefront passes through the phase characteristic-based optical focusingfilter such as the Fresnel zone plate, irradiance may be strengthened byconstructive interference at the focal point. As the plane wave-shapeddecrypted wavefront moves away from the focal point, irradiance may beweakened by destructive interference. Therefore, if the phase mask usedat the transmitter is accurately compensated through the inverse phasemask used at the receiver, the optical beam can be optimally collectedat the focal point through the Fresnel zone plate.

On the other hand, in the case of an interference signal caused byambient interference (i.e., in the case of interference from otheroptical resources), the phase characteristics of the optical beam can beconverted in the receiver as shown in FIG. 29 . In FIG. 29 , it isassumed that the gray color denotes “Phase=0”, the black color denotes“Phase=π”, and the white color denotes “Phase=−π”. However, referring tothe Fresnel zone plate shown in FIG. 29 , the black color denotes aphysically blocked space (i.e., the optical resource cannot pass throughthe blocked space) regardless of the phase, and the white color denotesa physically opened space (i.e., the optical resource can pass throughthe opened space) regardless of the phase. The phase of the encryptedwavefront received in the receiver can be depicted in the (x, y)two-dimensional plane as shown in the left-first view of FIG. 29 . Inthe case of ambient interference, as the encrypted optical beam affectedby ambient interference passes through the inverse phase mask (see theleft-second view of FIG. 29 ) not corresponding to thespecific-patterned phase mask used in the transmitter, there may occurmismatch phase pattern information, resulting in formation of thedecrypted wavefront corresponding to the left-third view of FIG. 29 . Inother words, the wavefront plane is depicted as a wavefront having adifferent pattern in a wavefront composed of the specific pattern, andmay have a random phase pattern. Since the signal affected by ambientinterference does not use the inverse phase mask matched with the phasepattern used at the transmitter, the phase incident upon the Fresnelzone plate can be expressed as shown in FIG. 30 .

In other words, in the plane waves having the same phase, as thewavefront having a random phase is incident upon the Fresnel zone plateby which optical focusing is performed at the focal point, the focusingfunction is lost, and destructive interference occurs in the focalplane, so that irradiance can be dispersed. When the decrypted wavefrontof the random pattern passes through the phase characteristic—basedoptical focusing filter such as a Fresnel zone plate, irradiancecharacteristics of the focused beam incident upon the O-to-E device(e.g., a photodiode) may appear as shown in FIG. 31 .

In FIG. 31 , the left view represents a focused beam represented by the(x, y) two-dimensional plane. In FIG. 31 , the white color denotes thearea of the optical beam having the strongest irradiance, and the blackcolor denotes the area of the optical beam having the weakestirradiance. When the intensity of irradiance is represented by theZ-axis, the intensity of irradiance can be expressed as athree-dimensional (3D) irradiance as shown in the middle view of FIG. 31. An example of measuring the intensity of irradiance is shown in theright view of FIG. 31 . That is, when the decrypted wavefront formed ina random phase pattern shape passes through the phasecharacteristic-based optical focusing filter such as the Fresnel zoneplate, irradiance may be weakened by destructive interference at thetotal focal plane. Therefore, the phase mask used at the transmitter andthe inverse phase mask of the receiver are used differently, therebyminimizing undesired interference from the focal plane through theFresnel zone plate. In this case, the desired optical beam can maximizethe amount of desired information at the focal point, because the phasemask is matched between the transmitter and the receiver. That is, whena signal causing interference and a desired signal are receivedtogether, a signal to interference ratio (SIR) for the desired signaland the interference signal can be maximized. Based on the irradianceobtained from the experimental data shown in FIG. 31 , a difference inpeak magnitude between the desired signal and the interference signalrepresents a difference of about 500 times.

On the other hand, the influence of sunlight can also be reduced in asimilar way to those of FIG. 31 . In the case of interference from thesunlight (i.e., the sun), the phase characteristics of the optical beamcan be converted at the receiver as shown in FIG. 32 .

In the case of sunlight interference, as the wavefront having plane wavecharacteristics passes through the inverse phase mask (see theleft-second view of FIG. 32 ), the resultant wavefront becomes awavefront in which the phase pattern information of the inverse phasemask is decrypted as it is, resulting in formation of a decryptedwavefront corresponding to the left-third view of FIG. 32 . In otherwords, in the plane waves having the same phase, as the wavefront havinga phase pattern designed as the inverse phase mask is incident upon theFresnel zone plate by which optical focusing is performed at the focalpoint, the focusing function is lost, and destructive interferenceoccurs in the focal plane, so that irradiance of the focused beamincident upon the O-to-E device (e.g., the photodiode) appears as shownin FIG. 33 .

In more detail, when the decrypted wavefront formed in a phase patternshape corresponding to the inverse phase mask passes through the phasecharacteristic-based optical focusing filter such as the Fresnel zoneplate, irradiance may be weakened by destructive interference at thetotal focal plane. Therefore, if the inverse phase mask of the receiveris applied to an arbitrary interference signal (such as sunlight) thatis not encrypted, undesired interference can be minimized on the focalplane through the Fresnel zone plate. In this case, the desired opticalbeam can maximize desired information at the focal point because thephase mask is matched between the transmitter and the receiver. That is,when a signal causing interference and a desired signal are receivedtogether, a signal to interference ratio (SIR) for the desired signaland the interference signal can be maximized. Based on the irradianceobtained from the experimental data shown in FIG. 33 , a difference inpeak magnitude between the desired signal and the interference signalrepresents a difference of about 500 times.

3.3. Wavefront Encryption-Based Interference Mitigation for use inSystem using the OAM transceiver

According to the disclosure shown in the above-described Sections 3.1 to3.2, the system can operate equally even when orbital angular momentum(OAM) is applied to the optical beam transmitted from the transmitter.

In the system according to the present disclosure, according to thepredefined promise between the transmitter and the receiver, thetransmitter generates an OAM beam through the OAM generator and performswavefront encryption through the phase mask, and the receiver performswavefront decryption through the inverse phase mask of the phase maskapplied to the transmitter and mitigates interference by performingoptical focusing through the optical filter designed to use the phasecharacteristics.

FIG. 34 is a diagram illustrating the structure of a transceiver of aninterference mitigation system based on a wavefront encryption for usein the system designed to use the OAM transceiver. As can be seen fromthe beginning part of Section 2, the transmitter may convert data foroptical wireless communication into an optical resource, may convert theoptical resource into an OAM beam through the photon OAM beam generator,so that the phase pattern of the phase mask can be applied to a helicalwavefront having OAM characteristics. The desired optical beam havingpassed through the phase mask composed of a specific pattern may havethe shape of the encrypted wavefront. For example, in the transmitter,the phase characteristics of the optical beam can be converted as shownin FIG. 35 .

In FIG. 35 , it is assumed that the gray color denotes “Phase=0”, theblack color denotes “Phase=π”, and the white color denotes “Phase=−π”.Assuming that the phase of the wavefront of the optical beam havingpassed through the E-to-O device and the OAM generator of thetransmitter is shown as a helical wave (e.g., Laguerre-Gaussian (LG)beam) that varies depending on the OAM order, the phase of the wavefrontcan be depicted in the (x, y) two-dimensional (2D) plane as shown in theleft view of FIG. 35 . When the optical beam passes through the phasemask (i.e., the middle view of FIG. 35 ) having a specific pattern, thedesired optical beam may have the shape of an encrypted wavefront asshown in the right view of FIG. 35 . That is, the wavefront plane isdepicted as a wavefront coupled to a specific pattern in the helicalwaves that varies depending on the OAM order.

In addition, as disclosed in Section 2 above, the receiver receives theencrypted optical beam and allows the beam to pass through the inversephase mask to compensate for the phase pattern used for encryption atthe transmitter, so that the encrypted wavefront can be converted intothe original helical wave. The original helical wave converted into theoriginal helical wave may perform optical focusing through an opticalfilter (e.g., a Fresnel zone plate, a photon sieve, etc.) designed touse phase characteristics. For example, in the receiver, the phasecharacteristics of the optical beam can be converted as shown in FIG. 36.

In FIG. 36 , it is assumed that the gray color denotes “Phase=0”, theblack color denotes “Phase=π”, and the white color denotes “Phase=−π”.However, referring to the Fresnel zone plate shown in FIG. 36 , theblack color denotes a physically blocked space (i.e., the opticalresource cannot pass through the blocked space) regardless of the phase,and the white color denotes a physically opened space (i.e., the opticalresource can pass through the opened space) regardless of the phase. Thephase of the encrypted wavefront received in the receiver can bedepicted in the (x, y) two-dimensional plane as shown in the left-firstview of FIG. 36 . When the encrypted optical beam passes through theinverse phase mask (i.e., the left-second view of FIG. 36 )corresponding to the specific-patterned phase mask used at thetransmitter, the encrypted optical beam may have the shape of adecrypted wavefront corresponding to the left-third view of FIG. 36 .That is, the wavefront plane is depicted as a helical wave in which thephase of a wavefront having a specific pattern varies depending on theOAM order. When the decrypted wavefront formed in the helical wavepasses through the phase characteristic—based optical focusing filtersuch as the Fresnel zone plate, there may appear irradiancecharacteristics of the focused beam incident upon the O-to-E device(e.g., the photodiode) as shown in FIG. 37 .

In FIG. 37 , the left view represents a focused beam represented by the(x, y) two-dimensional plane. In FIG. 37 , the white color denotes thearea of the optical beam having the strongest irradiance, and the blackcolor denotes the area of the optical beam having the weakestirradiance. When the intensity of irradiance is represented by theZ-axis, the intensity of irradiance can be expressed as athree-dimensional (3D) irradiance as shown in the middle view of FIG. 37. An example of measuring the intensity of irradiance is shown in theright view of FIG. 37 . That is, if the helical wave-shaped decryptedwavefront passes through the phase characteristic-based optical focusingfilter such as the Fresnel zone plate, irradiance may be strengthened byconstructive interference at the focal point. As the helical wave-shapeddecrypted wavefront moves away from the focal point, irradiance may beweakened by destructive interference. Therefore, if the phase mask usedat the transmitter is accurately compensated through the inverse phasemask used at the receiver, the optical beam can be optimally collectedat the focal point through the Fresnel zone plate.

On the other hand, in the same manner as described in Section 2, in thecase of ambient interference (i.e., interference from other opticalresources), since the encrypted optical beam from the ambientinterference passes through the inverse phase mask (the left-second viewof FIG. 38 ) not corresponding to the phase mask of the particularpattern used at the transmitter, phase pattern information is notmatched, so that the decrypted optical beam has the shape of a wavefronthaving a random phase.

In other words, in the helical wave varying depending on the OAM order,as the wavefront having a random phase is incident upon the Fresnel zoneplate by which optical focusing is performed at the focal point, thefocusing function is lost, and destructive interference occurs in thefocal plane, so that irradiance can be dispersed. When the decryptedwavefront formed in a random phase shape passes through the phasecharacteristic—based optical focusing filter such as a Fresnel zoneplate, irradiance characteristics of the focused beam incident upon theO-to-E device (e.g., a photodiode) may appear as shown in FIG. 39 .

Therefore, the phase mask used at the transmitter and the inverse phasemask of the receiver are used differently, thereby minimizing undesiredinterference from the focal plane through the Fresnel zone plate. Inthis case, the desired optical beam can maximize the amount of desiredinformation at the focal point, because the phase mask is matchedbetween the transmitter and the receiver. That is, when a signal causinginterference and a desired signal are received together, a signal tointerference ratio (SIR) for the desired signal and the interferencesignal can be maximized. Based on the irradiance obtained from theexperimental data shown in FIG. 39 , a difference in peak magnitudebetween the desired signal and the interference signal represents adifference of about 20 times.

3.4. Phase Mask Information Promise Between Transmitter andReceiver-Based on Control of Transmitter

3.4.1. Tx-Rx Initial Access Based on Legacy Link

The transmitter and the receiver may share initial information foroptical wireless communication through a legacy link (e.g., LTE, LTE-A,NR, Wi-Fi, Bluetooth, etc.). The initial information for opticalwireless communication may include phase mask information for encryptionand encryption period information.

3.4.2. Broadcast Message-based Tx-Rx Initial Access

The transmitter and the receiver broadcast a previously promisedbroadcast message over optical resources, such as a broadcast message(e.g., a PBCH of LTE/LTE A or a Common Control Channel), so that thetransmitter and the receiver may share initial information for opticalwireless communication. The initial information for optical wirelesscommunication may include phase mask information for encryption andencryption period information.

3.4.3. Phase Mask Information for Encryption

3.4.3.1. Referring to FIG. 40 , when the phase pattern information ofthe phase mask is previously shared as a look-up table, the transmittermay transmit only the index information for the phase pattern to thereceiver.

3.4.3.2. Referring to FIG. 41 , when the phase pattern information ofthe phase mask is not previously shared as the look-up table, thetransmitter may transmit look-up table information and index informationfor the phase pattern to the receiver.

3.4.3.3. Referring to FIG. 42 , when the phase pattern information ofthe phase mask is not previously shared as the look-up table, thetransmitter may transmit the entire information for the phase pattern tothe receiver.

3.4.3.4. Information on the phase mask may be a vector or a matrixconsisting of previously promised phase values. An example of the phasemask can be as follows.

3.4.3.4.1. P1=[0π0ππ0π; π00ππ00π; . . . ; 0ππ0π0π0], P2= . . . .

3.4.3.4.2. P1=[0 π/2 0 3π/2 −π/2 0 0 −π; −π/2 0 0 3π/2-3π/2 0 0 π; . . .; 0 π/2 π0 3π/2 0 −π0], P2= . . . .

3.4.3.4.3. On the other hand, distribution of the respectivecoefficients of a vector or a matrix consisting of previously promisedphase values may be denoted by uniform distribution (e.g., Gaussian orPoisson Distribution).

3.4.3.5. The phase mask look-up table may be comprised of phase masks ofthe following types.

3.4.3.5.1. Phase Masks having Various Physical Sizes

3.4.3.5.1.1. In order to perform encryption on the entire area of thepassed beam or encryption on a partial area, the phase mask may havedifferent physical sizes.

3.4.3.5.1.2. Considering that the size of the phase mask applied at thetransmitter is expanded by beam divergence in the receiver, thetransmitter may apply the phase mask to perform encryption on only apartial area.

3.4.3.5.1.3. In the above-described method, a phase change is appliedonly to a partial area and at the same time a phase change is notapplied to another partial area, thereby obtaining the same effects inboth partial areas. For example, in one case in which P1=[0 0 0 0; 0π−π0; 0 −ππ0; 0 0 0 0] is applied to the entire area, and in the othercase in which P2=[π−π; −ππ] is applied only to a partial area of thecenter of the beam, the same effects can be obtained.

3.4.4. Encryption Period Information

3.4.4.1. The time (that is, the encryption period) at which the phasemask for encryption is maintained (that is, the encryption period) canbe promised between the transmitter and the receiver in advanceaccording to the units (e.g., symbol, slot, subframe, frame, etc.)determined in the communication system.

3.4.4.2. The time (i.e., an encryption period) at which the phase maskfor encryption is maintained according to a predetermined time unit(e.g., several milliseconds, several seconds, several minutes, and thelike) can be promised between the transmitter and the receiver.

3.4.4.3. The above-described encryption period information may bedynamically controlled.

On the other hand, the above information may be used in an initialaccess step, and may be updated during communication including aconnection step or an intermittent connection step or the like. Inaddition, the disclosure in Section 4 above may be suitable for theenvironment in which the distance between the transmitter and thereceiver is relatively short, may be suitable for the environment inwhich the beam size can be maintained, or may be suitable for theenvironment in which the receiver can receive all of the surfaces of theentire beam.

3.5. Phase Mask Information Promise Between Transmitter andReceiver—Based on Measurement and Feedback of Receiver

Radio light has a beam divergence according to the characteristics ofoptical sources (optical/photon sources). Thus, depending on thedistance between the transmitter and the receiver, the size of the beamreceived at the receiver may be different. In order to address thisissue, there is a need for a method for performing wavefront encryptionin consideration of different sizes of beams received in the receiver.

3.5.1. Method for applying Encryption based on Feedback of Receiverafter measurement of Beam Divergence

3.5.1.1. The transmitter may transmit data with the desired optical beam(TEM₀₀ or TEM_(p1)) in a promised manner, as described above in Section1.

In this case, during transmission of the desired beam, the transmittermay transmit a periodic reference signal in a promised manner betweenthe transmitter and the receiver.

3.5.1.1.2. During transmission of the reference signal, the transmittermay transmit the reference signal in a situation where the phase mask isin the in-phase state over the entire wavefront, so that the transmittercan transmit only the complete reference signal.

3.5.1.2. As described in Section 1 above, the receiver may allow thedesired optical beam (TEM₀₀ or TEM_(p1)) to penetrate the optical filterin a promised manner, so that the transmitter can receive data.

3.5.1.2.1. At this time, when the reference signal is received, thereceiver may receive the reference signal in a situation where theinverse phase mask is in the in-phase state over the entire wavefront,so that the receiver can receive the complete reference signal affectedonly by the channel.

3.5.1.2.2. The receiver may measure a photodiode array area for adesired beam based on the reference signal to measure a beam radius.

3.5.1.2.2.1. The receiver may determine, among photodiodes correspondingto a desired beam, some photodiodes within a threshold based on averageintensity as desired photodiodes.

3.5.1.2.2.1.1. For example, a desired photodiode can be determinedaccording to the following conditions:

${{\frac{\left( {\Sigma_{p}^{❘D❘}{intensity}_{p}} \right)}{❘D❘} - {threshold}_{1}} < {{Desired}{Photodiode}} < {\frac{\left( {\Sigma_{p}^{❘D❘}{intensity}_{p}} \right)}{❘D❘} + {threshold}_{1}}},$

where p ∈ D.

3.5.1.2.2.1.2. D=Set of photodiodes corresponding to the desired beamzone

3.5.1.2.2.1.3. |D|=The number of photodiodes corresponding to thedesired beam zone

3.5.1.2.2.1.4. threshold_(I)=Intensity threshold that is predefined oradaptively established

3.5.1.2.3. The receiver may measure the beam radius (Rd) from thedetermined desired photodiodes.

3.5.1.2.3.1. Referring to FIG. 43 , the desired photodiodes may not bedistributed at the center (x0, y0) of the photodiode array, and thereceiver may infer the beam radius (Rd) based on the measured pattern.

3.5.1.3. The receiver feeds back the measured beam radius information tothe transmitter.

3.5.1.3.1. The receiver feeds back the beam radius information receivedthrough a feedback channel (e.g., PUCCH or PUSCH of LTE/LTE-A/NR) to thetransmitter.

3.5.1.3.2. The feedback information may be the radius information (Rd)of the desired beam and the reference coordinate (x_(n), y_(n)), and/ormay be the radius information (Ri) of the interference beam and thereference coordinate (x_(m), y_(m))

3.5.1.3.3. The feedback information may be transmitted in the form ofdata or may be transmitted as quantized information, or indexinformation may be transmitted by a predefined look-up table.

3.5.1.4. The transmitter may perform OAM mode selection and phase maskselection based on the feedback beam radius information.

3.5.1.4.1. OAM mode selection may be omitted from the system to whichOAM is not applied.

3.5.1.5. The transmitter generates an optical beam (TEM₀₀ or TEM_(p1))based on the selected OAM mode index, and allows the generated opticalbeam to pass through the phase mask, so that the transmitter cantransmit the resultant beam to the receiver.

3.5.1.5.1. In a system to which OAM is not applied, the beam (TEM₀₀) (ora general optical beam) is generated.

3.5.1.6. The receiver may allow the encrypted desired optical beam(TEM₀₀ or TEM_(p1)) to pass through the inverse phase mask and theoptical filter using the method promised in Sections 1 to 2, so that theO-to-E device can receive the resultant beam.

3.5.1.7. The above-described operation may be defined in advance in thesystem or may be periodically performed according to a specific periodestablished by the transmitter.

3.5.1.8. The above-described operation can be performed aperiodically ordynamically in consideration of decryption performance (e.g., packetdrop rate or block error rate) at the transmitter or the receiver.

3.5.1.8.1. The reference value of decryption performance may bepredefined or adaptively selected.

3.5.2. Method in which, in a situation where encryption is applied, thereceiver measures beam divergence and feeds back the measured result.

3.5.2.1. The transmitter encrypts the desired optical beam (TEM₀₀ orTEM_(p1)) using the phase mask in a method promised in Section 2, andtransmits encrypted data.

3.5.2.1.1. At this time, when the transmitter transmits the desiredbeam, the transmitter may transmit a periodic reference signal in apromised manner between the transmitter and the receiver.

3.5.2.1.2. During transmission of the reference signal, the transmittertransmits the encrypted reference signal corresponding to a signal thathas passed through the phase mask.

3.5.2.2. The receiver may decrypt the encrypted desired optical beam(TEM₀₀ or TEM_(p1)) using the inverse phase mask in a promised methoddescribed in Section 3, and may allow the decrypted result to passthrough the optical filter to receive data.

3.5.2.2.1. In this case, upon receiving the reference signal, thereceiver may receive the reference signal that has penetrated theinverse phase mask, so that the receiver can receive the decryptedreference signal in which the influence of the channel remains.

3.5.2.2.1.1. The influence of the channel may be compensated based onthe adaptive optics or based on channel information stored in previousdata reception.

3.5.2.2.2. The receiver may measure the photodiode array area for thedesired beam based on the reference signal, so that the beam radius canbe measured.

3.5.2.2.2.1. Since there is no accurate information on beam divergence,the receiver may repeatedly acquire the most suitable scaling factor byscaling the phase mask. For example, as shown in FIG. 44 , the receiveris designed to use the inverse phase mask for the entire area or apartial area of the promised phase mask while sequentially changing theunit in the order from the smallest scaling unit to the largest scalingunit.

3.5.2.2.2.1.1. In this case, the above-described repetitive operationcan be performed by simultaneously splitting energy for one signalthrough a beam splitter.

3.5.2.2.2.2. When the beam having penetrated the inverse phase maskapplied in a situation where the scaling unit is repeatedly changed, thereceiver may have the largest peak energy at the focal point or mayselect the scaling factor having the largest energy throughout the focalplane.

3.5.2.2.2.3. Based on the selected scaling factor, the receiver maymeasure the beam radius and the distance between the transmitter and thereceiver.

3.5.2.2.3. On the other hand, when the scaling factor of the inversephase mask is obtained by the method described above in Section 5.2.2.2,the receiver may establish the inverse phase mask by applying theobtained scaling factor to the inverse phase mask without performing theprocedure of Section 5.2.3, which will be described later (that is,without feedback), thereby receiving data.

3.5.2.3. The receiver feeds back the measured beam radius information ordistance information to the transmitter.

3.5.2.3.1. The receiver feeds back the beam radius information receivedat the transmitter through a feedback channel (e.g., a PUCCH or PUSCH ofLTE/LTE-A/NR) of a feedback channel.

3.5.2.3.2. The feedback information may be the radius information (Rd)of the desired beam and the reference coordinates (x_(n), y_(n)), and/ormay be the radius information (Ri) of the interference beam and thereference coordinates (x_(m), y_(m)).

3.5.2.3.3. The feedback information may be transmitted in the form ofdata or may be transmitted as quantized information, or indexinformation may be transmitted by a predefined look-up table.

3.5.2.4. The transmitter may perform OAM mode selection and phase maskselection based on the feedback beam radius information.

3.5.2.4.1. OAM mode selection may be omitted from the system to whichOAM is not applied.

3.5.2.5. The transmitter may generate an optical beam (TEM₀₀ orTEM_(p1)) based on the selected OAM mode index, and may allow thegenerated beam to pass through the phase mask, so that the resultantbeam can be transmitted to the receiver.

3.5.2.5.1. In a system to which OAM is not applied, the beam (TEM₀₀) (ora general optical beam) is generated.

3.5.2.6. The receiver may allow the encrypted desired optical beam(TEM₀₀ or TEM_(p1)) to pass through the inverse phase mask and theoptical filter using the method promised in Sections 1 to 2, so that theO-to-E device can receive the resultant beam.

3.5.2.7. The above-described operation may be defined in advance in thesystem or may be periodically performed according to a specific periodestablished by the transmitter.

3.5.2.8. The above-described operation can be performed aperiodically ordynamically in consideration of decryption performance (e.g., packetdrop rate or block error rate) at the transmitter or the receiver.

3.5.2.9. The reference value of decryption performance may be predefinedor adaptively selected.

On the other hand, the transmitter and the receiver performing theprocedures of Sections 5.1 and 5.2 and the operation thereof are asshown in FIG. 45 .

3.5.3. Phase mask Selection through Distance Measurement based onSensing

3.5.3.1. The transmitter may encrypt the desired optical beam (TEM₀₀ orTEM_(p1)) using a phase mask in a method promised in Section 3, and maytransmit encrypted data.

3.5.3.1.1. At this time, when the transmitter transmits the desiredbeam, the transmitter may transmit a periodic reference signal in apromised manner between the transmitter and the receiver.

3.5.3.2. The transmitter may measure the distance to a target receiver(target Rx) target using a distance measurement sensor (for example, aRADAR (radar detection and ranging) algorithm, and a LiDAR (lightdetection and ranging) algorithm.

3.5.3.3. The transmitter may perform OAM mode selection and phase maskselection based on the measured distance information.

3.5.3.3.1. The OAM mode selection may be omitted from the system towhich OAM is not applied.

3.5.3.4. The transmitter may generate an optical beam (TEM₀₀ orTEM_(p1)) based on the selected OAM mode index, and may allow thegenerated beam to pass through the phase mask, so that the resultantbeam can be transmitted to the receiver.

3.5.3.4.1. In a system to which OAM is not applied, the beam (TEM₀₀) (ora general optical beam) can be generated.

3.5.3.5. The receiver may allow the encrypted desired optical beam(TEM₀₀ or TEM_(p1)) to pass through the inverse phase mask and theoptical filter using the method promised in Sections 1 to 2, so that theO-to-E device can receive the resultant beam.

3.5.3.6. The above-described operation may be defined in advance in thesystem or may be periodically performed according to a specific periodestablished by the transmitter.

3.5.3.7. The above-described operation can be performed aperiodically ordynamically in consideration of decryption performance (e.g., packetdrop rate or block error rate) at the transmitter or the receiver.

3.5.3.8. The reference value of decryption performance may be predefinedor adaptively selected.

On the other hand, the transmitter and the receiver performing theprocedures of Section 5.3, and the operation thereof are as shown inFIG. 46 .

3.5.4. Phase Mask Selection through Distance Measurement based onFeedback and Sensing

3.5.4.1. Based on the beginning part of Sections 3.5.1 to 3.5.3described above, the transmitter and the receiver may combine thefeedback information and the sensing information as shown in FIG. 47 toadaptively select the optimal OAM mode index and the optimal phase maskindex, so that the selected information can be utilized for informationtransmission. On the other hand, in a system to which OAM is notapplied, OAM mode selection can be omitted. The transmitter and thereceiver performing the procedures of Section 5.4, and the operationthereof are as shown in FIG. 47 . The method according to the presentdisclosure shown in FIG. 47 may be suitable for the environment in whichthe distance between the transmitter and the receiver is relatively longso that the beam is spread out, or may be suitable for the environmentin which the receiver cannot receive all of the surfaces of the entirebeam.

When the wavefront encryption system of Sections 3.1 to 3.5 isimplemented, the configuration of a phase mask may vary depending on thesize of a single phase shifter constituting the phase mask. If the sizeof the phase shifter is large, it may be difficult to finely control thephase mask used to encrypt the wavefront of a target signal.

Due to a change in the distance between the transmitter and thereceiver, it may be difficult to match a phase mask used to encrypt adesired signal from the transmitter with an inverse phase mask used bythe receiver to decrypt the desired signal. For example, it may benecessary to accurately match the inverse phase mask to decode thereceived signal without loss. However, the distance and location maychange due to the mobility of the transmitter or receiver, the wavefrontencrypted by the phase mask may be misaligned with the inverse phasemask. If the wavefront and the inverse phase mask are misaligned, thedecoding performance of the receiver may be reduced. As the size of aphase shifter constituting the phase mask decreases, the matchingaccuracy may be sensitive. As the size of the phase shifter increases,the matching accuracy may become insensitive.

In other words, the phase mask needs to be designed considering thecharacteristics of the phase mask and inverse phase mask. That is, aspecific phase mask design needs to be agreed between the transmitterand receiver.

Hereinafter, a method of designing a quantized phase mask to performencryption on a wavefront based on a phase mask in optical wirelesscommunication will be described.

4.1. Quantization Order

For a technique of performing encryption on a wavefront based on a phasemask, the phase mask may need to be implemented with a phase shifterhaving the following characteristics: diffraction, refraction, andreflection based on optical elements. To control a phase mask (orinverse phase mask) used by the receiver that matches with a phase maskused by the transmitter, a quantization configuration method for thephase mask and a phase mask determination method between the transmitterand receiver are proposed. The phase mask used by the transmitter mayinclude phase shifters.

4.1.1 Quantization Order Q

The quantization order refers to a unit for dividing the wavefront areaof a desired transmission beam or reception beam. The entire beam may bedivided by the square of the quantization order, resulting in a singlequantization beam. As shown in FIG. 48 , when the area of the entirebeam is divided by the square of the quantization order, the area of asingle quantization beam may be obtained. The same phase is applied tothe single quantization beam.

FIG. 48 shows the phases of a phase mask plotted on a two-dimensionalplane of (x, y). In FIG. 48 , the phase of a portion marked in black (ora portion having relatively low brightness) is −π, and the phase of aportion marked in white (or a portion with relatively high brightness)is 0. In the example of FIG. 48 , the quantization order Q is 25, andthe total beam area is composed of 25{circumflex over ( )}2 singlequantized beams. If the size of a transmitted desired beam is the sameas the size of the phase mask of FIG. 28 , the wavefront of the desiredbeam may be encrypted based on the phase mask of FIG. 28 .

FIG. 49 shows exemplary phase masks depending on the quantization orderQ.

In FIG. 49 , the phase of a portion marked in black (or a portion havingrelatively low brightness) is −π, and the phase of a portion marked inwhite (or a portion with relatively high brightness) is 0.

Referring to FIG. 49 , as the size of Q increases, the area of the samewavefront may be further divided. That is, the area of the singlequantization beam becomes smaller as the size of Q increases.

Assuming that the z-axis shown in FIG. 50 is the time axis, an opticalbeam in the form of a plane wave may pass through a phase mask thatchanges the phase based on the delay. The optical beam may travel in thepositive direction of the z-axis. As shown in FIG. 50 , an encryptedwavefront may be composed of wavefronts whose phases are changedaccording to the delay characteristic of the phase mask.

In FIG. 50 , a part of the beam passing through a medium having a delayof b may have a non-zero phase, and a part of the beam passing through amedium having a length shorter than that of the medium having a delay ofb may have a phase shifted by −π. The medium having the shorter lengthmay have a length corresponding to a delay of a. A part of the beampassing through a medium having a length longer than that of the mediumhaving a delay of b may have a phase shifted by π. The medium having thelonger length may have a length corresponding to a delay of c. Althoughnot shown in FIG. 50 , since the phase shift is applied to both thex-axis and the y-axis, the optical beam is encrypted according to thephase pattern in terms of the (x, y) two-dimensional plane of thewavefront.

The phase mask may be formed as a set of multiple phase shifters. Theset of multiple phase shifters may be, for example, a phase shifterarray. In addition, the phase mask may be formed so that the shape of aphase shifter partially performs another phase shifter. In order topartially perform the other phase shifter, a structure in which thephase of a reflected optical beam is deformed when the optical beam isirradiated to a hologram may be used as an optical element based on ahologram pattern.

4.1.2 Selection of Quantization Order Q

4.1.4.1. The larger the size of Q, the stronger the encryptionperformance. In other words, the finer the quantization of the phasemask, the stronger the encryption performance. The reason for this isthat as the size of Q increases, the focusing ability related to the useof an inaccurate inverse phase mask decreases.

4.1.2.2. The larger the size of Q, the stronger the interferenceattenuation performance of an encryption-based interference cancellationtechnology for the wavefront. In other words, the finer the quantizationof the phase mask, the stronger the interference attenuation performanceof the encryption-based interference cancellation technology for thewavefront. The reason for this is that as the size of Q increases, thephase matching inaccuracy between the inverse phase mask and interferingbeam increases, and thus, the SIR increases due to a decrease in thefocusing ability, compared to the desired beam.

4.1.2.3. As the size of Q increases, the size of a required single phaseshifter decreases, and thus the implementation complexity increases. Inother words, as the quantization of the phase mask becomes finer, thesize of the required single phase shifter decreases, and thus, theimplementation complexity increases. This is because the number ofquantized beams to be implemented within the same area increases as thesize of Q increases.

4.1.2.4. As the size of Q increases, the beam alignment performancerequired for the transmitter and receiver increases. In other words, asthe quantization of the phase mask becomes finer, the beam alignmentperformance required for the transmitter and receiver becomes higher.This is because the beam alignment mismatch between the transmitter andreceiver affects the alignment performance of the phase mask of thetransmitter and the alignment performance of the inverse phase mask ofthe receiver.

4.2 Phase Pattern

4.2.1 Phase Order P

4.2.1.1 For the phase order P, if the pattern of the phase mask is θ₁,the phase is

$\theta_{i} = {{- \pi} + {\frac{\left( {i - 1} \right)}{P}.}}$

2π, where i is an integer greater than or equal to 1 and smaller than orequal to P.

For example, if P=2, θ₁=−π, and θ₂=0.

For example, if P=3, θ₁=−π, θ₂=−(½)π, and θ₃=(½)π.

For example, if P=4, θ₁=−π, θ₂=−(½)π, θ₃=0, and θ₄=(½)π.

For example, if P=16, θ₁=−π, θ₂=−(⅞)π, θ₃=−( 6/8)π, θ₄=−(⅝)π, θ₅=−(4/8)π, 06=−(⅜)π, θ₇=−( 2/8)π, Os=−(⅛)π, θ₉=0, θ₁₀=(⅛)π, θ₁₁=( 2/8)π,θ₁₂=(⅜)π, θ₁₃=( 4/8)π, θ₁₄=(⅝)π, θ₁₅=( 6/8)π, and θ₁₆=(⅞)π.

As shown in the examples, phase values may be evenly distributed forvarious values of P. Alternatively, the phase values may be unevenlydistributed for various values of P.

FIG. 51 shows wavefronts depending on the phase order P.

Referring to FIG. 51 , the phase of a portion marked in black (or aportion with relatively low brightness) is −π=01, which is the smallestphase value, and the phase of a portion marked in white (or a portionwith relatively high brightness) is 0=θ_(p), which is the largest phasevalue. The phase of a portion with brightness between black and white is0_(i), which increases as the brightness increases.

4.2.1.2. Selection of Phase Order P

4.2.1.2.1. The larger the size of P, the stronger the encryptionperformance. This is because as the size of P increases, the phase Oi ofthe phase mask is variously configured.

4.2.1.2.2. The larger the size of P, the stronger the interferenceattenuation performance of an encryption-based interference cancellationtechnology for the wavefront. The reason for this is that as the size ofP increases, the phase matching inaccuracy between the inverse phasemask and interfering beam increases, and thus, the SIR increases due toa decrease in the focusing ability, compared to the desired beam.

4.2.1.2.3. As the size of P increases, various phase shifters arerequired, and thus, the implementation complexity increases. This isbecause as the size of P increases, the phase mask is designed based onvarious phase shifters.

4.2.2. Phase Distribution

4.2.2.1. Uniform Distribution: The phase Oi of the phase mask may followthe uniform distribution. The uniform distribution may be used tomaximize the wavefront encryption or interference mitigation performanceon average.

4.2.2.2. Other Distributions including Gaussian Distribution and PoissonDistribution: The phase Oi of the phase mask may follow a predefineddistribution such as a Gaussian distribution and/or a Poissondistribution.

4.3. Phase Mask Generation

4.3.1. UE-specific Phase Mask Generation

4.3.1.1. In a cellular communication system such as LTE/LTE-A and NR, aunique UE ID may be assigned to each user in a cell. When the unique UEID is assigned to each user, a pseudo-random sequence based on the UE IDmay be generated with a length of Q{circumflex over ( )}2*log 2 (P)according to a rule predefined between the transmitter and receiver. Forexample, in the LTE system, the scrambling sequence of a PDSCH isgenerated based on a cell ID and a UE ID. A rule f (x) for generating apseudo-random sequence may be predefined between the transmitter andreceiver. For the rule of f (UE ID)=pseudo-random sequence (UE ID), apseudo-random sequence may have a sequence length of Q{circumflex over( )}2*log 2 (P). For the rule f (x), a conventional sequence generationmethod of LTE/LTE-A and NR systems may be used, or a new rule may bedefined.

4.3.1.2. By converting a generated sequence into a decimal numbercorresponding to the phase order P, a phase order vector having a sizeof (Q{circumflex over ( )}2)×1 may be generated.

4.3.1.3. By setting a coefficient of the generated phase order vector tothe i-1 value of the phase θ_(i) of the phase mask, a phase vectorhaving a size of (Q{circumflex over ( )}2)×1 may be generated with thephase θ_(i) corresponding to each coefficient.

4.3.1.4. The phase vector having a size of (Q{circumflex over ( )}2)×1may be generated by matching phase values according to a predeterminedrule to the two-dimensional plane of a quantized phase mask having asize of Q×Q.

4.3.1.5. FIGS. 52 to 54 show exemplary processes until the phase mask isgenerated based on the rule f (x) described in Section 4.3.1. FIG. 52shows a phase mask generation process in the case of P=2 and Q=4. FIG.53 shows a phase mask generation process in the case of P=4 and Q=2.FIG. 54 shows a phase mask generation process in the case of P=4 andQ=4. FIGS. 52 to 54 show that each phase vector is located in the phasemask. The position of the phase mask at which each value of 0; of thephase vector is mapped may vary according to transform rules.

4.3.2. Cell-specific Phase Mask Generation

4.3.2.1. In a cellular communication system such as LTE/LTE-A and NR, acell ID may be assigned to each cell. When the cell ID is assigned toeach cell, a pseudo-random sequence based on the cell ID may begenerated with a length of Q{circumflex over ( )}2*log 2 (P) by a rulepredefined between the transmitter and receiver. For example, a rule f(x) for generating a pseudo-random sequence may be predefined betweenthe transmitter and receiver. For the rule of f (cell ID)=pseudo-randomsequence (cell ID), the pseudo-random sequence may have a sequencelength of Q{circumflex over ( )}2*log 2 (P).

4.3.2.2. By converting a generated sequence into a decimal numbercorresponding to the phase order P, a phase order vector having a sizeof (Q{circumflex over ( )}2)×1 may be generated.

4.3.2.3. By setting a coefficient of the generated phase order vector tothe i-1 value of the phase θ_(i) of the phase mask, a phase vectorhaving a size of (Q{circumflex over ( )}2)×1 may be generated with thephase θ_(i) corresponding to each coefficient.

4.3.2.4. The phase vector having a size of (Q{circumflex over ( )}2)×1may be generated by matching phase values according to a predeterminedrule to the two-dimensional plane of a quantized phase mask having asize of Q×Q.

4.3.3. Predefined Phase Mask Look-up Table

4.3.3.1. A plurality of phase masks may be defined based on thepredefined look-up table.

4.3.3.2. The transmitter and receiver may select a phase mask from thelook-up table according to a predefined rule.

4.3.3.3. UE-specific Selection: In a cellular communication system suchas LTE/LTE-A and NR, a unique UE ID may be assigned to each user in acell. When the unique UE ID is assigned to each user, phase mask indexselection based on the UE ID may be performed according to a rulepredefined between the transmitter and receiver. For example, a phasemask index may be determined by the following operation: Phase MaskIndex=Mod (UE ID, Look up Table Size). To perform the phase maskselection in the entirety of the look-up table, the phase mask index maybe selected by performing the modulo operation on the UE ID and thelook-up table size.

4.3.3.4. Cell-specific Selection: In a cellular communication systemsuch as LTE/LTE-A and NR, a cell ID may be assigned to each cell. Whenthe cell ID is assigned to each cell, phase mask index selection basedon the cell ID may be performed according a rule predefined between thetransmitter and receiver. For example, a phase mask index may bedetermined by the following operation: Phase Mask Index=Mod (cell ID,Look-up Table Size). To perform the phase mask selection in the entiretyof the look-up table, the phase mask index may be selected by performingthe modulo operation on the cell ID and the look-up table size.

4.3.3.5. The transmitter uses a phase mask based on the selected phasemask index to perform wavefront encryption. The receiver uses a phasemask (and/or inverse phase mask) based on the selected phase mask indexto perform wavefront decoding.

4.4. Indication Rule

4.4.1. Phase mask information may be exchanged between the transmitterand the receiver in a UE-specific and/or cell-specific manner accordingto the method in Section 3.4. The phase mask information may furtherinclude the quantization order Q and the phase order P.

4.4.1.1. Selection of Parameters Q and P

4.4.1.1.1. Selection Depending on Interference Level: Considering thatthe interference dispersion effect needs to be improved as theinterference level increases, larger Q and/or P values need to beselected. As the interference level increases, the beam alignment needsto be performed more accurately.

4.4.1.1.2. Selection Depending on Distance: As the distance between thetransmitter and receiver decreases, the beam alignment may need to beperformed more accurately. If larger Q and/or P values are selected, theinterference dispersion effect may be improved.

4.4.1.1.3. Selection Depending on environment: In an environment wherethe channel variation increases, the beam alignment may need to beperformed more accurately. Smaller Q and/or P values may be selected inconsideration of the channel variation.

4.4.1.2. Indication of Parameters P and Q

4.4.1.2.1. The transmitter may select the parameters P and/or Q andprovide information about the parameters P and/or Q to the receiver asdescribed in Section 4.4.1.1. The transmitter and receiver may generatea sequence or select a phase mask index based on the provided parametersP and/or Q according to the methods described in Sections 4.3.1 to4.3.3. FIG. 55(a) shows an example in which the transmitter provides thereceiver with the information about the parameters P and/or Q andgenerates the sequence according to the methods described in Sections4.3.1 and/or 4.3.2. FIG. 55(b) shows an example of selecting the phasemask index from the look-up table as described in Section 4.3.3.

4.4.1.2.2. The receiver may select the parameters P and/or Q and provideinformation about the parameters P and/or Q to the transmitter asdescribed in Section 4.4.1.1. The transmitter and receiver may generatea sequence or select a phase mask index based on the provided parametersP and/or Q according to the methods described in Sections 4.3.1 to4.3.3. FIG. 56(a) shows an example in which the receiver provides thetransmitter with the information about the parameters P and/or Q andgenerates the sequence according to the methods described in Sections4.3.1 and/or 4.3.2. FIG. 56(b) shows an example of selecting the phasemask index from the look-up table as described in Section 4.3.3.

4.4.1.2.3. The transmitter and/or receiver may select the parameters Pand/or Q as described in Section 4.4.1.1. The transmitter and receivermay perform phase mask selection based on the provided parameters Pand/or Q. Among the transmitter and/or the receiver, a communicationdevice that performs the phase mask selection indicates and/or feedsback the index of the selected phase mask to the other communicationdevice. FIG. 57(a) shows an example in which the transmitter selects Pand/or Q, selects a phase mask, and informs the receiver of the selectedphase mask. FIG. 57(b) shows an example in which the receiver selects Pand/or Q, selects a phase mask, and informs the transmitter of theselected phase mask.

4.4.2. The phase mask information may be exchanged between thetransmitter and receiver UE-specifically and/or cell-specifically asdescribed in Section 3.4. The parameters Q and/or P may be reflected inthe phase mask look-up table preconfigured for the transmitter and/orreceiver.

4.4.3. The phase mask information may be exchanged between thetransmitter and receiver UE-specifically and/or cell-specifically asdescribed in Section 3.4. As the phase mask look-up table preconfiguredfor the transmitter and/or receiver, a phase mask look-up table for Qand a phase mask look-up table for P may exist, respectively. Thetransmitter and/or receiver may select a look-up table according to theindicated quantization order Q and/or phase order P.

5. Interference Dispersion Performance Depending on

FIG. 58 shows an exemplary structure of the receiver.

For example, sunlight may act as an interference signal. When theinverse phase mask of the receiver is applied to sunlight, theinterference dispersion effect may appear as shown in FIG. 59 dependingon the value of Q. The application of the inverse phase mask shown inFIG. 59 corresponds to a case where the phase mask of the transmitter isnot applied. Referring to FIG. 59 , as the size of Q increases, theencryption-based interference of the wavefront is mitigated. In otherwords, as the quantization of the phase mask becomes finer, theencryption-based interference of the wavefront is mitigated.

For example, a Gaussian beam may act as an interference signal. When theinverse phase mask of the receiver is applied to the Gaussian beam, theinterference dispersion effect may appear as shown in FIG. 60 dependingon the value of Q. The application of the inverse phase mask shown inFIG. 60 corresponds to a case where the phase mask of the transmitter isnot applied. Referring to FIG. 60 , as the size of Q increases, theencryption-based interference of the wavefront is mitigated. In otherwords, as the quantization of the phase mask becomes finer, theencryption-based interference of the wavefront is mitigated.

For example, an LG beam may act as an interference signal. When theinverse phase mask of the receiver is applied to the LG beam, theinterference dispersion effect may appear as shown in FIG. 61 dependingon the value of Q. The application of the inverse phase mask shown inFIG. 61 corresponds to a case where the phase mask of the transmitter isnot applied. Referring to FIG. 60 , as the size of Q increases, theencryption-based interference of the wavefront is mitigated. In otherwords, as the quantization of the phase mask becomes finer, theencryption-based interference of the wavefront is mitigated.

In this specification, quantization is shown in a square shape forconvenience of description, but the area of a part or the entirety of abeam may be quantized in other shapes or units.

In this specification, the method for performing optical focusing basedon the phase-front characteristics of an optical beam (or signal) todistinguish interference from a desired signal has been described basedon LG and OAM beams, but the method may be applied to other opticalbeams having the phase-front characteristics. For example, forHermite-Gaussian (HG) modes and/or TEM_(mn) having rectangulartransverse mode patterns, interference may be distinguished from adesired signal according to the method described in the presentdisclosure. The phase-front characteristics of an HG beam have arectangular phase change as in the LG beam, instead of having a circularphase change. For example, the intensity and phase of the LG or HG beammay be formed according to the values of modes ‘pl’ and‘mn’ as shown inFIG. 62 .

Therefore, for the HG beam, a desired signal may be focused in the formshown in FIG. 63 after passing through an optical filter for performingoptical focusing, based on the phase characteristics described herein. Aplane on which the desired signal is focused after the optical filtermay be a focal plane.

Accordingly, the embodiments described herein may be applied to allother types of optical beams as long as the beams have a phasedifference in the phase front.

The application of the embodiments described herein may be dynamicallydetermined depending on whether the communication device recognizesinterference. For example, operations according to at least one of theembodiments described herein may be initiated for interferencecancellation and/or interference isolation only when the transmitterand/or receiver recognizes interference. If the transmitter and/orreceiver fails to recognize interference or if the amount of recognizedinterference is less than or equal to a threshold, the operationsaccording to at least one of the embodiments described herein may not beperformed. For example, FIG. 64 shows a case in which the transmitterand/or receiver determines whether to activate a specific operation byrecognizing interference and/or comparing the interference with athreshold.

6.1 Phase Mask Selection Based on Interference Recognition

6.1.1 Phase Mask Selection Based on Interference Recognition byTransmitter

6.1.1.1. FIG. 64(a) shows an example in which the transmitter recognizesinterference and selects a phase mask. The transmitter detects and/ormeasures the interference according to a predetermined method. Thepredetermined method may be, for example, a method of recognizing anoptical resource around a transmitter/receiver link in terms of energydetection to perceive interference.

6.1.1.2. The transmitter determines whether to use a phase mask based onthe recognized interference information. When the interference is lessthan a predefined threshold or when there is no interference, the effectof the interference on a desired signal is small even if the phase maskis not used, so that decoding of the desired signal may be allowed.Therefore, when the interference is less than the predefined thresholdor when there is no interference, the transmitter may determine not touse the phase mask.

6.1.1.3. Control information for optical wireless communication may beshared through a legacy link. The legacy link may include, for example,at least one of legacy wireless communication schemes such as LTE,LTE-A, NR, Wi-Fi, and Bluetooth. Alternatively, the control informationfor wireless optical communication may be shared by broadcasting abroadcast message on an optical resource. The broadcast message may be,for example, a predefined broadcast message such as a PBCH or commoncontrol channel of LTE/LTE-A. The control information for wirelessoptical communication may include information on enabling and/ordisabling of the phase mask.

6.1.1.4. The receiver determines whether to use the phase mask based onthe received control information.

6.1.1.5. The desired signal is transmitted and received between thetransmitter and receiver based on information on the use of the phasemask determined by the phase mask selection of the transmitter and/orreceiver.

6.1.2. Phase Mask Selection Based on Interference Recognition byReceiver

6.1.2.1. FIG. 64(b) shows an example in which the receiver recognizesinterference and selects a phase mask. The receiver detects and/ormeasures the interference according to a predetermined method. Thepredetermined method may be, for example, a method of recognizing anoptical resource around a transmitter/receiver link in terms of energydetection to perceive interference.

6.1.2.2. The receiver may transmit and/or feed back the perceivedinterference information to the transmitter. The interferenceinformation may be, for example, information on the presence or absenceof the interference and/or information on the magnitude of interferencequantized based on a predefined threshold.

6.1.2.3. The transmitter determines whether to use the phase mask basedon the received interference information. When the interference is lessthan the predefined threshold or when there is no interference, theeffect of the interference on a desired signal is small even without theuse of the phase mask, so that decoding of the desired signal may beallowed. Therefore, when the interference is less than the predefinedthreshold or when there is no interference, the transmitter maydetermine not to use the phase mask.

6.1.2.3. Control information for optical wireless communication may beshared through a legacy link. The legacy link may include, for example,at least one of legacy wireless communication schemes such as LTE,LTE-A, NR, Wi-Fi, and Bluetooth. Alternatively, the control informationfor wireless optical communication may be shared by broadcasting abroadcast message on an optical resource. The broadcast message may be,for example, a predefined broadcast message such as a PBCH or commoncontrol channel of LTE/LTE-A. The control information for wirelessoptical communication may include information on enabling and/ordisabling of the phase mask.

6.1.1.4. The receiver determines whether to use the phase mask based onthe received control information.

6.1.1.5. The desired signal is transmitted and received between thetransmitter and receiver based on information on the use of the phasemask determined by the phase mask selection of the transmitter and/orreceiver.

The receiver may determine by itself whether to use the phase mask ornot. The receiver may determine whether to use the phase mask and thentransmit and/or feed back information on enabling and/or disabling ofthe phase mask to the transmitter. The transmitter may transmit thedesired signal to the receiver based on the received information in astate that the phase mask is enabled and/or disabled.

Implementation Examples

The embodiments of the present disclosure may be implemented byorganically combining at least one of the above-described operations.

In FIG. 65 , one of the embodiments implemented by a combination of theabove-described operations is illustrated. The operations of FIG. 65 maybe performed by the transmitter mentioned in this document, and thetransmitter may include the BS and/or UE shown in FIG. 1 . In FIG. 65 ,the transmitter may be referred to as a first communication device, andthe receiver may be referred to as a second communication device.

The first communication device may apply a phase pattern to thewavefront of an optical signal (S6501) and transmit the optical signalto which the phase pattern is applied to the second communication device(S6503). From the perspective of the second communication device,although not shown, the operations of FIG. 65 may be interpreted asfollows. The second communication device may receive from the firstcommunication device the optical signal where the phase pattern isapplied to the wavefront and then decode the received optical signal.

The phase pattern applied to the wavefront of the optical signal may bedetermined based on optical phase shift characteristics of a phase mask.In this case, the phase mask may be determined based on a quantizationorder and a phase order. The quantization order Q refers to a unit fordividing the wavefront area of a desired transmission or reception beamas described in Section 4.1. The phase order P refers to the phase ofthe phase mask as described in Section 4.2.

The phase mask may be generated as described in Section 4.3 inconsideration of the advantages/disadvantages of each value of P and/orQ described in Sections 4.1 and 4.2. For example, the phase mask may begenerated based on the ID of the first communication device or generatedbased on the ID of the second communication device. Since the firstcommunication device may be the UE or BS, and the second communicationdevice may also be the UE or BS. The phase mask may be generated basedon a UE ID as described in Section 4.3.1 or generated based on a cell IDas described in Section 4.3.2. In addition, the phase mask may begenerated based on a look-up table as in Section 4.4.3.

The quantization order and phase order, which are the basis forgenerating the phase mask, may (i) be selected by the firstcommunication device or (ii) selected by the second communication deviceand received by the first communication device as described in Section4.4. The quantization order and phase order may be selectedUE-specifically and/or cell-specifically. In addition, one or morelook-up tables for the quantization order and/or phase order may bepreconfigured for the first and second communication devices.

Although the phase mask may always be used by the communication devices,it may be desirable to use the phase mask only when interference to adesired optical signal is greater than or equal to a threshold. Theinterference measurement method and subject may follow the descriptionin Section 6.1.1. For example, the interference may be measured byrecognizing an optical resource around a transmitter/receiver link interms of energy detection. The interference may (i) be measured by thefirst communication device or (ii) be measured by the secondcommunication device and received by the first communication device. Inaddition, instead of transmitting the measured interference to the firstcommunication device, the second communication device may determine byitself whether to use the phase mask and then transmit to the firstcommunication device information on the determination whether the phasemask is used. The information on whether the phase mask is used may (i)be transmitted according to a communication method other than opticalwireless communication or (ii) be broadcast through the wireless opticalcommunication.

The operations described with reference to FIG. 65 may be additionallyperformed in combination with at least one of the operations describedwith reference to FIGS. 1 to 64 .

The wireless optical communication described in this document may beapplied to various fields such as artificial intelligence, robots, andautonomous vehicles.

The above-described embodiments correspond to combinations of elementsand features of the present disclosure in prescribed forms. And, therespective elements or features may be considered as selective unlessthey are explicitly mentioned. Each of the elements or features can beimplemented in a form failing to be combined with other elements orfeatures. Moreover, it is able to implement an embodiment of the presentdisclosure by combining elements and/or features together in part. Asequence of operations explained for each embodiment of the presentdisclosure can be modified. Some configurations or features of oneembodiment can be included in another embodiment or can be substitutedfor corresponding configurations or features of another embodiment. And,it is apparently understandable that an embodiment is configured bycombining claims failing to have relation of explicit citation in theappended claims together or can be included as new claims by amendmentafter filing an application.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The present disclosure is industrially applicable to various wirelesscommunication systems such as 3GPP LTE/LTE-A and 5G systems.

1. A method of transmitting and receiving a signal by a firstcommunication device in optical wireless communication, the methodcomprising: applying a phase pattern to a wavefront of a signal, whereinthe signal is transmitted in a frequency range of visible light,ultraviolet, or infrared; and transmitting the signal to a secondcommunication device, wherein the signal is a physical downlink controlchannel (PDCCH), a physical uplink control channel (PUCCH), a physicaldownlink shared channel (PDSCH) or physical uplink shared channel(PUSCH), wherein the PDCCH includes downlink control information (DCI),wherein the DCI includes information about cell configuration, downlinkscheduling, or uplink grant, wherein the PUCCH includes uplink controlinformation (UCI), and the UCI includes acknowledgement, negativeacknowledgement, channel state information (CSI), or scheduling request(SR), wherein the phase pattern is determined based on optical phaseshift characteristics of a phase mask, and wherein the phase mask isdetermined based on a quantization order and a phase order.
 2. Themethod of claim 1, wherein the quantization order and the phase orderare (i) selected by the first communication device or (ii) selected bythe second communication device and received by the first communicationdevice.
 3. The method of claim 1, wherein the phase mask is determinedbased on (i) an identifier (ID) of the first communication device or(ii) an ID of the second communication device.
 4. The method of claim 1,wherein the phase mask is used based on interference to the signal beinggreater than or equal to a threshold, and wherein the interference is(i) measured by the first communication device or (ii) measured by thesecond communication device and received from the second communicationdevice.
 5. The method of claim 4, wherein information on whether thephase mask is used is (i) transmitted according to a communicationmethod other than the optical wireless communication or (ii) broadcastthrough the optical wireless communication.
 6. A first communicationdevice configured to transmit and receive a signal in a wirelesscommunication system, the first communication device comprising: atleast one transceiver; at least one processor; and at least one memoryoperably connected to the at least one processor and configured to storeinstructions that, when executed, cause the at least one processor toperform operations comprising: applying a phase pattern to a wavefrontof a signal, wherein the signal is transmitted in a frequency range ofvisible light, ultraviolet, or infrared; and transmitting the signal toa second communication device, wherein the signal is a physical downlinkcontrol channel (PDCCH), a physical uplink control channel (PUCCH), aphysical downlink shared channel (PDSCH) or physical uplink sharedchannel (PUSCH), wherein the PDCCH includes downlink control information(DCI), wherein the DCI includes information about cell configuration,downlink scheduling, or uplink grant, wherein the PUCCH includes uplinkcontrol information (UCI), and the UCI includes acknowledgement,negative acknowledgement, channel state information, or schedulingrequest, wherein the phase pattern is determined based on optical phaseshift characteristics of a phase mask, and wherein the phase mask isdetermined based on a quantization order and a phase order.
 7. The firstcommunication device of claim 6, wherein the quantization order and thephase order are (i) selected by the first communication device or (ii)selected by the second communication device and received by the firstcommunication device.
 8. The first communication device of claim 6,wherein the phase mask is determined based on (i) an identifier (ID) ofthe first communication device or (ii) an ID of the second communicationdevice.
 9. The first communication device of claim 6, wherein the phasemask is used based on interference to the signal being greater than orequal to a threshold, and wherein the interference is (i) measured bythe first communication device or (ii) measured by the secondcommunication device and received from the second communication device.10. The first communication device of claim 9, wherein information onwhether the phase mask is used is (i) transmitted according to acommunication method other than optical wireless communication or (ii)broadcast through the optical wireless communication.
 11. An apparatusfor a first communication device, the apparatus comprising: at least oneprocessor; and at least one computer memory operably connected to the atleast one processor and configured to, when executed, cause the at leastone processor to perform operations comprising: applying a phase patternto a wavefront of a signal, wherein the signal is transmitted in afrequency range of visible light, ultraviolet, or infrared; andtransmitting the signal to a second communication device, wherein thesignal is a physical downlink control channel (PDCCH), a physical uplinkcontrol channel (PUCCH), a physical downlink shared channel (PDSCH) orphysical uplink shared channel (PUSCH), wherein the PDCCH includesdownlink control information (DCI), wherein the DCI includes informationabout cell configuration, downlink scheduling, or uplink grant, whereinthe PUCCH includes uplink control information (UCI), and the UCIincludes acknowledgement, negative acknowledgement, channel stateinformation, or scheduling request, wherein the phase pattern isdetermined based on optical phase shift characteristics of a phase mask,and wherein the phase mask is determined based on a quantization orderand a phase order.
 12. The apparatus of claim 11, wherein thequantization order and the phase order are (i) selected by the apparatusor (ii) selected by the other apparatus and received by the apparatus.13. The apparatus of claim 11, wherein the phase mask is determinedbased on (i) an identifier (ID) of the first communication device or(ii) an ID of the second communication device.
 14. The apparatus ofclaim 11, wherein the phase mask is used based on interference to thesignal being greater than or equal to a threshold, and wherein theinterference is (i) measured by the apparatus or (ii) measured by theother apparatus and received from the other apparatus.
 15. The apparatusof claim 14, wherein information on whether the phase mask is used is(i) transmitted according to a communication method other than opticalwireless communication or (ii) broadcast through the optical wirelesscommunication.